bolt/cursor.go

package bolt

// TODO: #define CURSOR_STACK		 32

// TODO: #define C_INITIALIZED	0x01	/**< cursor has been initialized and is valid */
// TODO: #define C_EOF	0x02			/**< No more data */
// TODO: #define C_SUB	0x04			/**< Cursor is a sub-cursor */
// TODO: #define C_DEL	0x08			/**< last op was a cursor_del */
// TODO: #define C_SPLITTING	0x20		/**< Cursor is in page_split */
// TODO: #define C_UNTRACK	0x40		/**< Un-track cursor when closing */

// TODO: #define MDB_NOSPILL	0x8000 /** Do not spill pages to disk if txn is getting full, may fail instead */

type Cursor interface {
	First() error
	FirstDup() error
	Get() ([]byte, []byte, error)
	GetRange() ([]byte, []byte, error)
	Current() ([]byte, []byte, error)
	Last()
	LastDup()
	Next() ([]byte, []byte, error)
	NextDup() ([]byte, []byte, error)
	NextNoDup() ([]byte, []byte, error)
	Prev() ([]byte, []byte, error)
	PrevDup() ([]byte, []byte, error)
	PrevNoDup() ([]byte, []byte, error)
	Set() ([]byte, []byte, error)
	SetRange() ([]byte, []byte, error)
}

type cursor struct {
	flags       int
	_next       *cursor
	backup      *cursor
	xcursor     *xcursor
	transaction *transaction
	bucketId    int
	bucket      *Bucket
	// bucketx     *bucketx
	bucketFlag int
	snum       int
	top        int
	page       []*page
	ki         []int /**< stack of page indices */
}

type xcursor struct {
	cursor cursor
	bucket *Bucket
	// bucketx    *bucketx
	bucketFlag int
}

// Set or clear P_KEEP in dirty, non-overflow, non-sub pages watched by txn.
// @param[in] mc A cursor handle for the current operation.
// @param[in] pflags Flags of the pages to update:
// P_DIRTY to set P_KEEP, P_DIRTY|P_KEEP to clear it.
// @param[in] all No shortcuts. Needed except after a full #mdb_page_flush().
// @return 0 on success, non-zero on failure.
func (c *cursor) xkeep(pflags int, all int) error {
	/*
		enum { Mask = P_SUBP|P_DIRTY|P_KEEP };
		MDB_txn *txn = mc->mc_txn;
		MDB_cursor *m3;
		MDB_xcursor *mx;
		MDB_page *dp, *mp;
		MDB_node *leaf;
		unsigned i, j;
		int rc = MDB_SUCCESS, level;

		// Mark pages seen by cursors
		if (mc->mc_flags & C_UNTRACK)
			mc = NULL;				// will find mc in mt_cursors
		for (i = txn->mt_numdbs;; mc = txn->mt_cursors[--i]) {
			for (; mc; mc=mc->mc_next) {
				if (!(mc->mc_flags & C_INITIALIZED))
					continue;
				for (m3 = mc;; m3 = &mx->mx_cursor) {
					mp = NULL;
					for (j=0; j<m3->mc_snum; j++) {
						mp = m3->mc_pg[j];
						if ((mp->mp_flags & Mask) == pflags)
							mp->mp_flags ^= P_KEEP;
					}
					mx = m3->mc_xcursor;
					// Proceed to mx if it is at a sub-database
					if (! (mx && (mx->mx_cursor.mc_flags & C_INITIALIZED)))
						break;
					if (! (mp && (mp->mp_flags & P_LEAF)))
						break;
					leaf = NODEPTR(mp, m3->mc_ki[j-1]);
					if (!(leaf->mn_flags & F_SUBDATA))
						break;
				}
			}
			if (i == 0)
				break;
		}

		if (all) {
			// Mark dirty root pages
			for (i=0; i<txn->mt_numdbs; i++) {
				if (txn->mt_dbflags[i] & DB_DIRTY) {
					pgno_t pgno = txn->mt_dbs[i].md_root;
					if (pgno == P_INVALID)
						continue;
					if ((rc = mdb_page_get(txn, pgno, &dp, &level)) != MDB_SUCCESS)
						break;
					if ((dp->mp_flags & Mask) == pflags && level <= 1)
						dp->mp_flags ^= P_KEEP;
				}
			}
		}

		return rc;
	*/
	return nil
}

//	Spill pages from the dirty list back to disk.
// This is intended to prevent running into #MDB_TXN_FULL situations,
// but note that they may still occur in a few cases:
//	1) our estimate of the txn size could be too small. Currently this
//	 seems unlikely, except with a large number of #MDB_MULTIPLE items.
//	2) child txns may run out of space if their parents dirtied a
//	 lot of pages and never spilled them. TODO: we probably should do
//	 a preemptive spill during #mdb_txn_begin() of a child txn, if
//	 the parent's dirty_room is below a given threshold.
//
// Otherwise, if not using nested txns, it is expected that apps will
// not run into #MDB_TXN_FULL any more. The pages are flushed to disk
// the same way as for a txn commit, e.g. their P_DIRTY flag is cleared.
// If the txn never references them again, they can be left alone.
// If the txn only reads them, they can be used without any fuss.
// If the txn writes them again, they can be dirtied immediately without
// going thru all of the work of #mdb_page_touch(). Such references are
// handled by #mdb_page_unspill().
//
// Also note, we never spill DB root pages, nor pages of active cursors,
// because we'll need these back again soon anyway. And in nested txns,
// we can't spill a page in a child txn if it was already spilled in a
// parent txn. That would alter the parent txns' data even though
// the child hasn't committed yet, and we'd have no way to undo it if
// the child aborted.
//
// @param[in] m0 cursor A cursor handle identifying the transaction and
//	database for which we are checking space.
// @param[in] key For a put operation, the key being stored.
// @param[in] data For a put operation, the data being stored.
// @return 0 on success, non-zero on failure.
func (c *cursor) spill(key []byte, data []byte) error {
	/*
			MDB_txn *txn = m0->mc_txn;
			MDB_page *dp;
			MDB_ID2L dl = txn->mt_u.dirty_list;
			unsigned int i, j, need;
			int rc;

			if (m0->mc_flags & C_SUB)
				return MDB_SUCCESS;

			// Estimate how much space this op will take
			i = m0->mc_db->md_depth;
			// Named DBs also dirty the main DB
			if (m0->mc_dbi > MAIN_DBI)
				i += txn->mt_dbs[MAIN_DBI].md_depth;
			// For puts, roughly factor in the key+data size
			if (key)
				i += (LEAFSIZE(key, data) + txn->mt_env->me_psize) / txn->mt_env->me_psize;
			i += i;	// double it for good measure
			need = i;

			if (txn->mt_dirty_room > i)
				return MDB_SUCCESS;

			if (!txn->mt_spill_pgs) {
				txn->mt_spill_pgs = mdb_midl_alloc(MDB_IDL_UM_MAX);
				if (!txn->mt_spill_pgs)
					return ENOMEM;
			} else {
				// purge deleted slots
				MDB_IDL sl = txn->mt_spill_pgs;
				unsigned int num = sl[0];
				j=0;
				for (i=1; i<=num; i++) {
					if (!(sl[i] & 1))
						sl[++j] = sl[i];
				}
				sl[0] = j;
			}

			// Preserve pages which may soon be dirtied again
			if ((rc = mdb_pages_xkeep(m0, P_DIRTY, 1)) != MDB_SUCCESS)
				goto done;

			// Less aggressive spill - we originally spilled the entire dirty list,
			// with a few exceptions for cursor pages and DB root pages. But this
			// turns out to be a lot of wasted effort because in a large txn many
			// of those pages will need to be used again. So now we spill only 1/8th
			// of the dirty pages. Testing revealed this to be a good tradeoff,
			// better than 1/2, 1/4, or 1/10.
			if (need < MDB_IDL_UM_MAX / 8)
				need = MDB_IDL_UM_MAX / 8;

			// Save the page IDs of all the pages we're flushing
			// flush from the tail forward, this saves a lot of shifting later on.
			for (i=dl[0].mid; i && need; i--) {
				MDB_ID pn = dl[i].mid << 1;
				dp = dl[i].mptr;
				if (dp->mp_flags & P_KEEP)
					continue;
				// Can't spill twice, make sure it's not already in a parent's
				// spill list.
				if (txn->mt_parent) {
					MDB_txn *tx2;
					for (tx2 = txn->mt_parent; tx2; tx2 = tx2->mt_parent) {
						if (tx2->mt_spill_pgs) {
							j = mdb_midl_search(tx2->mt_spill_pgs, pn);
							if (j <= tx2->mt_spill_pgs[0] && tx2->mt_spill_pgs[j] == pn) {
								dp->mp_flags |= P_KEEP;
								break;
							}
						}
					}
					if (tx2)
						continue;
				}
				if ((rc = mdb_midl_append(&txn->mt_spill_pgs, pn)))
					goto done;
				need--;
			}
			mdb_midl_sort(txn->mt_spill_pgs);

			// Flush the spilled part of dirty list
			if ((rc = mdb_page_flush(txn, i)) != MDB_SUCCESS)
				goto done;

			// Reset any dirty pages we kept that page_flush didn't see
			rc = mdb_pages_xkeep(m0, P_DIRTY|P_KEEP, i);

		done:
			txn->mt_flags |= rc ? MDB_TXN_ERROR : MDB_TXN_SPILLS;
			return rc;
			/*
			return 0
		}

		// Allocate page numbers and memory for writing.  Maintain me_pglast,
		// me_pghead and mt_next_pgno.
		//
		// If there are free pages available from older transactions, they
		// are re-used first. Otherwise allocate a new page at mt_next_pgno.
		// Do not modify the freedB, just merge freeDB records into me_pghead[]
		// and move me_pglast to say which records were consumed.  Only this
		// function can create me_pghead and move me_pglast/mt_next_pgno.
		// @param[in] mc cursor A cursor handle identifying the transaction and
		//	database for which we are allocating.
		// @param[in] num the number of pages to allocate.
		// @param[out] mp Address of the allocated page(s). Requests for multiple pages
		//  will always be satisfied by a single contiguous chunk of memory.
		// @return 0 on success, non-zero on failure.
		func (c *cursor) allocPage(int num, MDB_page **mp) {
			int rc, retry = INT_MAX;
			MDB_txn *txn = mc->mc_txn;
			MDB_env *env = txn->mt_env;
			pgno_t pgno, *mop = env->me_pghead;
			unsigned i, j, k, mop_len = mop ? mop[0] : 0, n2 = num-1;
			MDB_page *np;
			txnid_t oldest = 0, last;
			MDB_cursor_op op;
			MDB_cursor m2;

			*mp = NULL;

			// If our dirty list is already full, we can't do anything
			if (txn->mt_dirty_room == 0) {
				rc = MDB_TXN_FULL;
				goto fail;
			}

			for (op = MDB_FIRST;; op = MDB_NEXT) {
				MDB_val key, data;
				MDB_node *leaf;
				pgno_t *idl, old_id, new_id;

				// Seek a big enough contiguous page range. Prefer
				// pages at the tail, just truncating the list.
				if (mop_len > n2) {
					i = mop_len;
					do {
						pgno = mop[i];
						if (mop[i-n2] == pgno+n2)
							goto search_done;
					} while (--i > n2);
					if (Max_retries < INT_MAX && --retry < 0)
						break;
				}

				if (op == MDB_FIRST) {	// 1st iteration
					// Prepare to fetch more and coalesce
					oldest = mdb_find_oldest(txn);
					last = env->me_pglast;
					mdb_cursor_init(&m2, txn, FREE_DBI, NULL);
					if (last) {
						op = MDB_SET_RANGE;
						key.mv_data = &last; // will look up last+1
						key.mv_size = sizeof(last);
					}
				}

				last++;
				// Do not fetch more if the record will be too recent
				if (oldest <= last)
					break;
				rc = mdb_cursor_get(&m2, &key, NULL, op);
				if (rc) {
					if (rc == MDB_NOTFOUND)
						break;
					goto fail;
				}
				last = *(txnid_t*)key.mv_data;
				if (oldest <= last)
					break;
				np = m2.mc_pg[m2.mc_top];
				leaf = NODEPTR(np, m2.mc_ki[m2.mc_top]);
				if ((rc = mdb_node_read(txn, leaf, &data)) != MDB_SUCCESS)
					return rc;

				idl = (MDB_ID *) data.mv_data;
				i = idl[0];
				if (!mop) {
					if (!(env->me_pghead = mop = mdb_midl_alloc(i))) {
						rc = ENOMEM;
						goto fail;
					}
				} else {
					if ((rc = mdb_midl_need(&env->me_pghead, i)) != 0)
						goto fail;
					mop = env->me_pghead;
				}
				env->me_pglast = last;
		#if (MDB_DEBUG) > 1
				DPRINTF(("IDL read txn %"Z"u root %"Z"u num %u",
					last, txn->mt_dbs[FREE_DBI].md_root, i));
				for (k = i; k; k--)
					DPRINTF(("IDL %"Z"u", idl[k]));
		#endif
				// Merge in descending sorted order
				j = mop_len;
				k = mop_len += i;
				mop[0] = (pgno_t)-1;
				old_id = mop[j];
				while (i) {
					new_id = idl[i--];
					for (; old_id < new_id; old_id = mop[--j])
						mop[k--] = old_id;
					mop[k--] = new_id;
				}
				mop[0] = mop_len;
			}

			// Use new pages from the map when nothing suitable in the freeDB
			i = 0;
			pgno = txn->mt_next_pgno;
			if (pgno + num >= env->me_maxpg) {
					DPUTS("DB size maxed out");
					rc = MDB_MAP_FULL;
					goto fail;
			}

		search_done:
			if (env->me_flags & MDB_WRITEMAP) {
				np = (MDB_page *)(env->me_map + env->me_psize * pgno);
			} else {
				if (!(np = mdb_page_malloc(txn, num))) {
					rc = ENOMEM;
					goto fail;
				}
			}
			if (i) {
				mop[0] = mop_len -= num;
				// Move any stragglers down 
				for (j = i-num; j < mop_len; )
					mop[++j] = mop[++i];
			} else {
				txn->mt_next_pgno = pgno + num;
			}
			np->mp_pgno = pgno;
			mdb_page_dirty(txn, np);
			*mp = np;

			return MDB_SUCCESS;

		fail:
			txn->mt_flags |= MDB_TXN_ERROR;
			return rc;
	*/
	return nil
}

// Copy the used portions of a non-overflow page.
// @param[in] dst page to copy into
// @param[in] src page to copy from
// @param[in] psize size of a page
func (p *page) copyTo(dst *page, size int) {
	/*
		enum { Align = sizeof(pgno_t) };
		indx_t upper = src->mp_upper, lower = src->mp_lower, unused = upper-lower;

		// If page isn't full, just copy the used portion. Adjust
		// alignment so memcpy may copy words instead of bytes.
		if ((unused &= -Align) && !IS_LEAF2(src)) {
			upper &= -Align;
			memcpy(dst, src, (lower + (Align-1)) & -Align);
			memcpy((pgno_t *)((char *)dst+upper), (pgno_t *)((char *)src+upper),
				psize - upper);
		} else {
			memcpy(dst, src, psize - unused);
		}
	*/
}

// Touch a page: make it dirty and re-insert into tree with updated pgno.
// @param[in] mc cursor pointing to the page to be touched
// @return 0 on success, non-zero on failure.
func (c *cursor) page_touch() int {
	/*
			MDB_page *mp = mc->mc_pg[mc->mc_top], *np;
			MDB_txn *txn = mc->mc_txn;
			MDB_cursor *m2, *m3;
			pgno_t	pgno;
			int rc;

			if (!F_ISSET(mp->mp_flags, P_DIRTY)) {
				if (txn->mt_flags & MDB_TXN_SPILLS) {
					np = NULL;
					rc = mdb_page_unspill(txn, mp, &np);
					if (rc)
						goto fail;
					if (np)
						goto done;
				}
				if ((rc = mdb_midl_need(&txn->mt_free_pgs, 1)) ||
					(rc = mdb_page_alloc(mc, 1, &np)))
					goto fail;
				pgno = np->mp_pgno;
				DPRINTF(("touched db %d page %"Z"u -> %"Z"u", DDBI(mc),
					mp->mp_pgno, pgno));
				mdb_cassert(mc, mp->mp_pgno != pgno);
				mdb_midl_xappend(txn->mt_free_pgs, mp->mp_pgno);
				// Update the parent page, if any, to point to the new page
				if (mc->mc_top) {
					MDB_page *parent = mc->mc_pg[mc->mc_top-1];
					MDB_node *node = NODEPTR(parent, mc->mc_ki[mc->mc_top-1]);
					SETPGNO(node, pgno);
				} else {
					mc->mc_db->md_root = pgno;
				}
			} else if (txn->mt_parent && !IS_SUBP(mp)) {
				MDB_ID2 mid, *dl = txn->mt_u.dirty_list;
				pgno = mp->mp_pgno;
				// If txn has a parent, make sure the page is in our
				// dirty list.
				if (dl[0].mid) {
					unsigned x = mdb_mid2l_search(dl, pgno);
					if (x <= dl[0].mid && dl[x].mid == pgno) {
						if (mp != dl[x].mptr) { // bad cursor?
							mc->mc_flags &= ~(C_INITIALIZED|C_EOF);
							txn->mt_flags |= MDB_TXN_ERROR;
							return MDB_CORRUPTED;
						}
						return 0;
					}
				}
				mdb_cassert(mc, dl[0].mid < MDB_IDL_UM_MAX);
				// No - copy it
				np = mdb_page_malloc(txn, 1);
				if (!np)
					return ENOMEM;
				mid.mid = pgno;
				mid.mptr = np;
				rc = mdb_mid2l_insert(dl, &mid);
				mdb_cassert(mc, rc == 0);
			} else {
				return 0;
			}

			mdb_page_copy(np, mp, txn->mt_env->me_psize);
			np->mp_pgno = pgno;
			np->mp_flags |= P_DIRTY;

		done:
			// Adjust cursors pointing to mp
			mc->mc_pg[mc->mc_top] = np;
			m2 = txn->mt_cursors[mc->mc_dbi];
			if (mc->mc_flags & C_SUB) {
				for (; m2; m2=m2->mc_next) {
					m3 = &m2->mc_xcursor->mx_cursor;
					if (m3->mc_snum < mc->mc_snum) continue;
					if (m3->mc_pg[mc->mc_top] == mp)
						m3->mc_pg[mc->mc_top] = np;
				}
			} else {
				for (; m2; m2=m2->mc_next) {
					if (m2->mc_snum < mc->mc_snum) continue;
					if (m2->mc_pg[mc->mc_top] == mp) {
						m2->mc_pg[mc->mc_top] = np;
						if ((mc->mc_db->md_flags & MDB_DUPSORT) &&
							m2->mc_ki[mc->mc_top] == mc->mc_ki[mc->mc_top])
						{
							MDB_node *leaf = NODEPTR(np, mc->mc_ki[mc->mc_top]);
							if (!(leaf->mn_flags & F_SUBDATA))
								m2->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(leaf);
						}
					}
				}
			}
			return 0;

		fail:
			txn->mt_flags |= MDB_TXN_ERROR;
			return rc;
	*/

	return 0
}

// Search for key within a page, using binary search.
// Returns the smallest entry larger or equal to the key.
// If exactp is non-null, stores whether the found entry was an exact match
// in *exactp (1 or 0).
// Updates the cursor index with the index of the found entry.
// If no entry larger or equal to the key is found, returns NULL.
func (c *cursor) search(key []byte) (*node, bool) {
	/*
			unsigned int	 i = 0, nkeys;
			int		 low, high;
			int		 rc = 0;
			MDB_page *mp = mc->mc_pg[mc->mc_top];
			MDB_node	*node = NULL;
			MDB_val	 nodekey;
			MDB_cmp_func *cmp;
			DKBUF;

			nkeys = NUMKEYS(mp);

			DPRINTF(("searching %u keys in %s %spage %"Z"u",
			    nkeys, IS_LEAF(mp) ? "leaf" : "branch", IS_SUBP(mp) ? "sub-" : "",
			    mdb_dbg_pgno(mp)));

			low = IS_LEAF(mp) ? 0 : 1;
			high = nkeys - 1;
			cmp = mc->mc_dbx->md_cmp;

			// Branch pages have no data, so if using integer keys,
			// alignment is guaranteed. Use faster mdb_cmp_int.
			if (cmp == mdb_cmp_cint && IS_BRANCH(mp)) {
				if (NODEPTR(mp, 1)->mn_ksize == sizeof(size_t))
					cmp = mdb_cmp_long;
				else
					cmp = mdb_cmp_int;
			}

			if (IS_LEAF2(mp)) {
				nodekey.mv_size = mc->mc_db->md_pad;
				node = NODEPTR(mp, 0);	// fake
				while (low <= high) {
					i = (low + high) >> 1;
					nodekey.mv_data = LEAF2KEY(mp, i, nodekey.mv_size);
					rc = cmp(key, &nodekey);
					DPRINTF(("found leaf index %u [%s], rc = %i",
					    i, DKEY(&nodekey), rc));
					if (rc == 0)
						break;
					if (rc > 0)
						low = i + 1;
					else
						high = i - 1;
				}
			} else {
				while (low <= high) {
					i = (low + high) >> 1;

					node = NODEPTR(mp, i);
					nodekey.mv_size = NODEKSZ(node);
					nodekey.mv_data = NODEKEY(node);

					rc = cmp(key, &nodekey);
		#if MDB_DEBUG
					if (IS_LEAF(mp))
						DPRINTF(("found leaf index %u [%s], rc = %i",
						    i, DKEY(&nodekey), rc));
					else
						DPRINTF(("found branch index %u [%s -> %"Z"u], rc = %i",
						    i, DKEY(&nodekey), NODEPGNO(node), rc));
		#endif
					if (rc == 0)
						break;
					if (rc > 0)
						low = i + 1;
					else
						high = i - 1;
				}
			}

			if (rc > 0) {	// Found entry is less than the key.
				i++;	// Skip to get the smallest entry larger than key.
				if (!IS_LEAF2(mp))
					node = NODEPTR(mp, i);
			}
			if (exactp)
				*exactp = (rc == 0 && nkeys > 0);
			// store the key index
			mc->mc_ki[mc->mc_top] = i;
			if (i >= nkeys)
				// There is no entry larger or equal to the key.
				return NULL;

			// nodeptr is fake for LEAF2
			return node;
	*/
	return nil, false
}

func (c *cursor) pop() {
	/*
			if (mc->mc_snum) {
		#if MDB_DEBUG
				MDB_page	*top = mc->mc_pg[mc->mc_top];
		#endif
				mc->mc_snum--;
				if (mc->mc_snum)
					mc->mc_top--;

				DPRINTF(("popped page %"Z"u off db %d cursor %p", top->mp_pgno,
					DDBI(mc), (void *) mc));
			}
	*/
}

/** Push a page onto the top of the cursor's stack. */
func (c *cursor) push(p *page) error {
	/*
		DPRINTF(("pushing page %"Z"u on db %d cursor %p", mp->mp_pgno,
			DDBI(mc), (void *) mc));

		if (mc->mc_snum >= CURSOR_STACK) {
			mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
			return MDB_CURSOR_FULL;
		}

		mc->mc_top = mc->mc_snum++;
		mc->mc_pg[mc->mc_top] = mp;
		mc->mc_ki[mc->mc_top] = 0;

		return MDB_SUCCESS;
	*/
	return nil
}

// Finish #mdb_page_search() / #mdb_page_search_lowest().
// The cursor is at the root page, set up the rest of it.
func (c *cursor) searchRoot(key []byte, flags int) error {
	/*
		MDB_page	*mp = mc->mc_pg[mc->mc_top];
		int rc;
		DKBUF;

		while (IS_BRANCH(mp)) {
			MDB_node	*node;
			indx_t		i;

			DPRINTF(("branch page %"Z"u has %u keys", mp->mp_pgno, NUMKEYS(mp)));
			mdb_cassert(mc, NUMKEYS(mp) > 1);
			DPRINTF(("found index 0 to page %"Z"u", NODEPGNO(NODEPTR(mp, 0))));

			if (flags & (MDB_PS_FIRST|MDB_PS_LAST)) {
				i = 0;
				if (flags & MDB_PS_LAST)
					i = NUMKEYS(mp) - 1;
			} else {
				int	 exact;
				node = mdb_node_search(mc, key, &exact);
				if (node == NULL)
					i = NUMKEYS(mp) - 1;
				else {
					i = mc->mc_ki[mc->mc_top];
					if (!exact) {
						mdb_cassert(mc, i > 0);
						i--;
					}
				}
				DPRINTF(("following index %u for key [%s]", i, DKEY(key)));
			}

			mdb_cassert(mc, i < NUMKEYS(mp));
			node = NODEPTR(mp, i);

			if ((rc = mdb_page_get(mc->mc_txn, NODEPGNO(node), &mp, NULL)) != 0)
				return rc;

			mc->mc_ki[mc->mc_top] = i;
			if ((rc = mdb_cursor_push(mc, mp)))
				return rc;

			if (flags & MDB_PS_MODIFY) {
				if ((rc = mdb_page_touch(mc)) != 0)
					return rc;
				mp = mc->mc_pg[mc->mc_top];
			}
		}

		if (!IS_LEAF(mp)) {
			DPRINTF(("internal error, index points to a %02X page!?",
			    mp->mp_flags));
			mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
			return MDB_CORRUPTED;
		}

		DPRINTF(("found leaf page %"Z"u for key [%s]", mp->mp_pgno,
		    key ? DKEY(key) : "null"));
		mc->mc_flags |= C_INITIALIZED;
		mc->mc_flags &= ~C_EOF;

		return MDB_SUCCESS;
	*/
	return nil
}

// Search for the lowest key under the current branch page.
// This just bypasses a NUMKEYS check in the current page
// before calling mdb_page_search_root(), because the callers
// are all in situations where the current page is known to
// be underfilled.
func (c *cursor) searchLowest() error {
	/*
		MDB_page	*mp = mc->mc_pg[mc->mc_top];
		MDB_node	*node = NODEPTR(mp, 0);
		int rc;

		if ((rc = mdb_page_get(mc->mc_txn, NODEPGNO(node), &mp, NULL)) != 0)
			return rc;

		mc->mc_ki[mc->mc_top] = 0;
		if ((rc = mdb_cursor_push(mc, mp)))
			return rc;
		return mdb_page_search_root(mc, NULL, MDB_PS_FIRST);
	*/
	return nil
}

// Search for the page a given key should be in.
// Push it and its parent pages on the cursor stack.
// @param[in,out] mc the cursor for this operation.
// @param[in] key the key to search for, or NULL for first/last page.
// @param[in] flags If MDB_PS_MODIFY is set, visited pages in the DB
//   are touched (updated with new page numbers).
//   If MDB_PS_FIRST or MDB_PS_LAST is set, find first or last leaf.
//   This is used by #mdb_cursor_first() and #mdb_cursor_last().
//   If MDB_PS_ROOTONLY set, just fetch root node, no further lookups.
// @return 0 on success, non-zero on failure.
func (c *cursor) findPage(key []byte, flags int) error {
	/*
		int		 rc;
		pgno_t		 root;

		// Make sure the txn is still viable, then find the root from
		// the txn's db table and set it as the root of the cursor's stack.
		if (F_ISSET(mc->mc_txn->mt_flags, MDB_TXN_ERROR)) {
			DPUTS("transaction has failed, must abort");
			return MDB_BAD_TXN;
		} else {
			// Make sure we're using an up-to-date root
			if (*mc->mc_dbflag & DB_STALE) {
					MDB_cursor mc2;
					mdb_cursor_init(&mc2, mc->mc_txn, MAIN_DBI, NULL);
					rc = mdb_page_search(&mc2, &mc->mc_dbx->md_name, 0);
					if (rc)
						return rc;
					{
						MDB_val data;
						int exact = 0;
						uint16_t flags;
						MDB_node *leaf = mdb_node_search(&mc2,
							&mc->mc_dbx->md_name, &exact);
						if (!exact)
							return MDB_NOTFOUND;
						rc = mdb_node_read(mc->mc_txn, leaf, &data);
						if (rc)
							return rc;
						memcpy(&flags, ((char *) data.mv_data + offsetof(MDB_db, md_flags)),
							sizeof(uint16_t));
						// The txn may not know this DBI, or another process may
						// have dropped and recreated the DB with other flags.
						if ((mc->mc_db->md_flags & PERSISTENT_FLAGS) != flags)
							return MDB_INCOMPATIBLE;
						memcpy(mc->mc_db, data.mv_data, sizeof(MDB_db));
					}
					*mc->mc_dbflag &= ~DB_STALE;
			}
			root = mc->mc_db->md_root;

			if (root == P_INVALID) {		// Tree is empty.
				DPUTS("tree is empty");
				return MDB_NOTFOUND;
			}
		}

		mdb_cassert(mc, root > 1);
		if (!mc->mc_pg[0] || mc->mc_pg[0]->mp_pgno != root)
			if ((rc = mdb_page_get(mc->mc_txn, root, &mc->mc_pg[0], NULL)) != 0)
				return rc;

		mc->mc_snum = 1;
		mc->mc_top = 0;

		DPRINTF(("db %d root page %"Z"u has flags 0x%X",
			DDBI(mc), root, mc->mc_pg[0]->mp_flags));

		if (flags & MDB_PS_MODIFY) {
			if ((rc = mdb_page_touch(mc)))
				return rc;
		}

		if (flags & MDB_PS_ROOTONLY)
			return MDB_SUCCESS;

		return mdb_page_search_root(mc, key, flags);
	*/
	return nil
}

func (c *cursor) freeOverflowPage(p *page) error {
	/*
			MDB_txn *txn = mc->mc_txn;
			pgno_t pg = mp->mp_pgno;
			unsigned x = 0, ovpages = mp->mp_pages;
			MDB_env *env = txn->mt_env;
			MDB_IDL sl = txn->mt_spill_pgs;
			MDB_ID pn = pg << 1;
			int rc;

			DPRINTF(("free ov page %"Z"u (%d)", pg, ovpages));
			// If the page is dirty or on the spill list we just acquired it,
			// so we should give it back to our current free list, if any.
			// Otherwise put it onto the list of pages we freed in this txn.
			//
			// Won't create me_pghead: me_pglast must be inited along with it.
			// Unsupported in nested txns: They would need to hide the page
			// range in ancestor txns' dirty and spilled lists.
			if (env->me_pghead &&
				!txn->mt_parent &&
				((mp->mp_flags & P_DIRTY) ||
				 (sl && (x = mdb_midl_search(sl, pn)) <= sl[0] && sl[x] == pn)))
			{
				unsigned i, j;
				pgno_t *mop;
				MDB_ID2 *dl, ix, iy;
				rc = mdb_midl_need(&env->me_pghead, ovpages);
				if (rc)
					return rc;
				if (!(mp->mp_flags & P_DIRTY)) {
					// This page is no longer spilled
					if (x == sl[0])
						sl[0]--;
					else
						sl[x] |= 1;
					goto release;
				}
				// Remove from dirty list
				dl = txn->mt_u.dirty_list;
				x = dl[0].mid--;
				for (ix = dl[x]; ix.mptr != mp; ix = iy) {
					if (x > 1) {
						x--;
						iy = dl[x];
						dl[x] = ix;
					} else {
						mdb_cassert(mc, x > 1);
						j = ++(dl[0].mid);
						dl[j] = ix;		// Unsorted. OK when MDB_TXN_ERROR.
						txn->mt_flags |= MDB_TXN_ERROR;
						return MDB_CORRUPTED;
					}
				}
				if (!(env->me_flags & MDB_WRITEMAP))
					mdb_dpage_free(env, mp);
		release:
				// Insert in me_pghead
				mop = env->me_pghead;
				j = mop[0] + ovpages;
				for (i = mop[0]; i && mop[i] < pg; i--)
					mop[j--] = mop[i];
				while (j>i)
					mop[j--] = pg++;
				mop[0] += ovpages;
			} else {
				rc = mdb_midl_append_range(&txn->mt_free_pgs, pg, ovpages);
				if (rc)
					return rc;
			}
			mc->mc_db->md_overflow_pages -= ovpages;
			return 0;
	*/
	return nil
}

// Find a sibling for a page.
// Replaces the page at the top of the cursor's stack with the
// specified sibling, if one exists.
// @param[in] mc The cursor for this operation.
// @param[in] move_right Non-zero if the right sibling is requested,
// otherwise the left sibling.
// @return 0 on success, non-zero on failure.
func (c *cursor) sibling(moveRight bool) error {
	/*
		int		 rc;
		MDB_node	*indx;
		MDB_page	*mp;

		if (mc->mc_snum < 2) {
			return MDB_NOTFOUND;		// root has no siblings
		}

		mdb_cursor_pop(mc);
		DPRINTF(("parent page is page %"Z"u, index %u",
			mc->mc_pg[mc->mc_top]->mp_pgno, mc->mc_ki[mc->mc_top]));

		if (move_right ? (mc->mc_ki[mc->mc_top] + 1u >= NUMKEYS(mc->mc_pg[mc->mc_top]))
			       : (mc->mc_ki[mc->mc_top] == 0)) {
			DPRINTF(("no more keys left, moving to %s sibling",
			    move_right ? "right" : "left"));
			if ((rc = mdb_cursor_sibling(mc, move_right)) != MDB_SUCCESS) {
				// undo cursor_pop before returning
				mc->mc_top++;
				mc->mc_snum++;
				return rc;
			}
		} else {
			if (move_right)
				mc->mc_ki[mc->mc_top]++;
			else
				mc->mc_ki[mc->mc_top]--;
			DPRINTF(("just moving to %s index key %u",
			    move_right ? "right" : "left", mc->mc_ki[mc->mc_top]));
		}
		mdb_cassert(mc, IS_BRANCH(mc->mc_pg[mc->mc_top]));

		indx = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
		if ((rc = mdb_page_get(mc->mc_txn, NODEPGNO(indx), &mp, NULL)) != 0) {
			// mc will be inconsistent if caller does mc_snum++ as above
			mc->mc_flags &= ~(C_INITIALIZED|C_EOF);
			return rc;
		}

		mdb_cursor_push(mc, mp);
		if (!move_right)
			mc->mc_ki[mc->mc_top] = NUMKEYS(mp)-1;

		return MDB_SUCCESS;
	*/
	return nil
}

// Move the cursor to the next data item.
func (c *cursor) next(key []byte, data []byte, op int) error {
	/*
			MDB_page	*mp;
			MDB_node	*leaf;
			int rc;

			if (mc->mc_flags & C_EOF) {
				return MDB_NOTFOUND;
			}

			mdb_cassert(mc, mc->mc_flags & C_INITIALIZED);

			mp = mc->mc_pg[mc->mc_top];

			if (mc->mc_db->md_flags & MDB_DUPSORT) {
				leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
				if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
					if (op == MDB_NEXT || op == MDB_NEXT_DUP) {
						rc = mdb_cursor_next(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_NEXT);
						if (op != MDB_NEXT || rc != MDB_NOTFOUND) {
							if (rc == MDB_SUCCESS)
								MDB_GET_KEY(leaf, key);
							return rc;
						}
					}
				} else {
					mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);
					if (op == MDB_NEXT_DUP)
						return MDB_NOTFOUND;
				}
			}

			DPRINTF(("cursor_next: top page is %"Z"u in cursor %p",
				mdb_dbg_pgno(mp), (void *) mc));
			if (mc->mc_flags & C_DEL)
				goto skip;

			if (mc->mc_ki[mc->mc_top] + 1u >= NUMKEYS(mp)) {
				DPUTS("=====> move to next sibling page");
				if ((rc = mdb_cursor_sibling(mc, 1)) != MDB_SUCCESS) {
					mc->mc_flags |= C_EOF;
					return rc;
				}
				mp = mc->mc_pg[mc->mc_top];
				DPRINTF(("next page is %"Z"u, key index %u", mp->mp_pgno, mc->mc_ki[mc->mc_top]));
			} else
				mc->mc_ki[mc->mc_top]++;

		skip:
			DPRINTF(("==> cursor points to page %"Z"u with %u keys, key index %u",
			    mdb_dbg_pgno(mp), NUMKEYS(mp), mc->mc_ki[mc->mc_top]));

			if (IS_LEAF2(mp)) {
				key->mv_size = mc->mc_db->md_pad;
				key->mv_data = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->mv_size);
				return MDB_SUCCESS;
			}

			mdb_cassert(mc, IS_LEAF(mp));
			leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);

			if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
				mdb_xcursor_init1(mc, leaf);
			}
			if (data) {
				if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
					return rc;

				if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
					rc = mdb_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
					if (rc != MDB_SUCCESS)
						return rc;
				}
			}

			MDB_GET_KEY(leaf, key);
			return MDB_SUCCESS;
	*/
	return nil
}

// Move the cursor to the previous data item.
func (c *cursor) prev(key []byte, data []byte, op int) error {
	/*
		MDB_page	*mp;
		MDB_node	*leaf;
		int rc;

		mdb_cassert(mc, mc->mc_flags & C_INITIALIZED);

		mp = mc->mc_pg[mc->mc_top];

		if (mc->mc_db->md_flags & MDB_DUPSORT) {
			leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
			if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
				if (op == MDB_PREV || op == MDB_PREV_DUP) {
					rc = mdb_cursor_prev(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_PREV);
					if (op != MDB_PREV || rc != MDB_NOTFOUND) {
						if (rc == MDB_SUCCESS)
							MDB_GET_KEY(leaf, key);
						return rc;
					}
				} else {
					mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);
					if (op == MDB_PREV_DUP)
						return MDB_NOTFOUND;
				}
			}
		}

		DPRINTF(("cursor_prev: top page is %"Z"u in cursor %p",
			mdb_dbg_pgno(mp), (void *) mc));

		if (mc->mc_ki[mc->mc_top] == 0)  {
			DPUTS("=====> move to prev sibling page");
			if ((rc = mdb_cursor_sibling(mc, 0)) != MDB_SUCCESS) {
				return rc;
			}
			mp = mc->mc_pg[mc->mc_top];
			mc->mc_ki[mc->mc_top] = NUMKEYS(mp) - 1;
			DPRINTF(("prev page is %"Z"u, key index %u", mp->mp_pgno, mc->mc_ki[mc->mc_top]));
		} else
			mc->mc_ki[mc->mc_top]--;

		mc->mc_flags &= ~C_EOF;

		DPRINTF(("==> cursor points to page %"Z"u with %u keys, key index %u",
		    mdb_dbg_pgno(mp), NUMKEYS(mp), mc->mc_ki[mc->mc_top]));

		if (IS_LEAF2(mp)) {
			key->mv_size = mc->mc_db->md_pad;
			key->mv_data = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->mv_size);
			return MDB_SUCCESS;
		}

		mdb_cassert(mc, IS_LEAF(mp));
		leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);

		if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
			mdb_xcursor_init1(mc, leaf);
		}
		if (data) {
			if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
				return rc;

			if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
				rc = mdb_cursor_last(&mc->mc_xcursor->mx_cursor, data, NULL);
				if (rc != MDB_SUCCESS)
					return rc;
			}
		}

		MDB_GET_KEY(leaf, key);
		return MDB_SUCCESS;
	*/
	return nil
}

// Set the cursor on a specific data item.
// (bool return is whether it is exact).
func (c *cursor) set(key []byte, data []byte, op int) (error, bool) {
	/*
			int		 rc;
			MDB_page	*mp;
			MDB_node	*leaf = NULL;
			DKBUF;

			if (key->mv_size == 0)
				return MDB_BAD_VALSIZE;

			if (mc->mc_xcursor)
				mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);

			// See if we're already on the right page
			if (mc->mc_flags & C_INITIALIZED) {
				MDB_val nodekey;

				mp = mc->mc_pg[mc->mc_top];
				if (!NUMKEYS(mp)) {
					mc->mc_ki[mc->mc_top] = 0;
					return MDB_NOTFOUND;
				}
				if (mp->mp_flags & P_LEAF2) {
					nodekey.mv_size = mc->mc_db->md_pad;
					nodekey.mv_data = LEAF2KEY(mp, 0, nodekey.mv_size);
				} else {
					leaf = NODEPTR(mp, 0);
					MDB_GET_KEY2(leaf, nodekey);
				}
				rc = mc->mc_dbx->md_cmp(key, &nodekey);
				if (rc == 0) {
					// Probably happens rarely, but first node on the page
					// was the one we wanted.
					mc->mc_ki[mc->mc_top] = 0;
					if (exactp)
						*exactp = 1;
					goto set1;
				}
				if (rc > 0) {
					unsigned int i;
					unsigned int nkeys = NUMKEYS(mp);
					if (nkeys > 1) {
						if (mp->mp_flags & P_LEAF2) {
							nodekey.mv_data = LEAF2KEY(mp,
								 nkeys-1, nodekey.mv_size);
						} else {
							leaf = NODEPTR(mp, nkeys-1);
							MDB_GET_KEY2(leaf, nodekey);
						}
						rc = mc->mc_dbx->md_cmp(key, &nodekey);
						if (rc == 0) {
							// last node was the one we wanted
							mc->mc_ki[mc->mc_top] = nkeys-1;
							if (exactp)
								*exactp = 1;
							goto set1;
						}
						if (rc < 0) {
							if (mc->mc_ki[mc->mc_top] < NUMKEYS(mp)) {
								// This is definitely the right page, skip search_page 
								if (mp->mp_flags & P_LEAF2) {
									nodekey.mv_data = LEAF2KEY(mp,
										 mc->mc_ki[mc->mc_top], nodekey.mv_size);
								} else {
									leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
									MDB_GET_KEY2(leaf, nodekey);
								}
								rc = mc->mc_dbx->md_cmp(key, &nodekey);
								if (rc == 0) {
									// current node was the one we wanted
									if (exactp)
										*exactp = 1;
									goto set1;
								}
							}
							rc = 0;
							goto set2;
						}
					}
					// If any parents have right-sibs, search.
					// Otherwise, there's nothing further.
					for (i=0; i<mc->mc_top; i++)
						if (mc->mc_ki[i] <
							NUMKEYS(mc->mc_pg[i])-1)
							break;
					if (i == mc->mc_top) {
						// There are no other pages
						mc->mc_ki[mc->mc_top] = nkeys;
						return MDB_NOTFOUND;
					}
				}
				if (!mc->mc_top) {
					// There are no other pages
					mc->mc_ki[mc->mc_top] = 0;
					if (op == MDB_SET_RANGE) {
						rc = 0;
						goto set1;
					} else
						return MDB_NOTFOUND;
				}
			}

			rc = mdb_page_search(mc, key, 0);
			if (rc != MDB_SUCCESS)
				return rc;

			mp = mc->mc_pg[mc->mc_top];
			mdb_cassert(mc, IS_LEAF(mp));

		set2:
			leaf = mdb_node_search(mc, key, exactp);
			if (exactp != NULL && !*exactp) {
				// MDB_SET specified and not an exact match.
				return MDB_NOTFOUND;
			}

			if (leaf == NULL) {
				DPUTS("===> inexact leaf not found, goto sibling");
				if ((rc = mdb_cursor_sibling(mc, 1)) != MDB_SUCCESS)
					return rc;		// no entries matched
				mp = mc->mc_pg[mc->mc_top];
				mdb_cassert(mc, IS_LEAF(mp));
				leaf = NODEPTR(mp, 0);
			}

		set1:
			mc->mc_flags |= C_INITIALIZED;
			mc->mc_flags &= ~C_EOF;

			if (IS_LEAF2(mp)) {
				key->mv_size = mc->mc_db->md_pad;
				key->mv_data = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->mv_size);
				return MDB_SUCCESS;
			}

			if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
				mdb_xcursor_init1(mc, leaf);
			}
			if (data) {
				if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
					if (op == MDB_SET || op == MDB_SET_KEY || op == MDB_SET_RANGE) {
						rc = mdb_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
					} else {
						int ex2, *ex2p;
						if (op == MDB_GET_BOTH) {
							ex2p = &ex2;
							ex2 = 0;
						} else {
							ex2p = NULL;
						}
						rc = mdb_cursor_set(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_SET_RANGE, ex2p);
						if (rc != MDB_SUCCESS)
							return rc;
					}
				} else if (op == MDB_GET_BOTH || op == MDB_GET_BOTH_RANGE) {
					MDB_val d2;
					if ((rc = mdb_node_read(mc->mc_txn, leaf, &d2)) != MDB_SUCCESS)
						return rc;
					rc = mc->mc_dbx->md_dcmp(data, &d2);
					if (rc) {
						if (op == MDB_GET_BOTH || rc > 0)
							return MDB_NOTFOUND;
						rc = 0;
						*data = d2;
					}

				} else {
					if (mc->mc_xcursor)
						mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);
					if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
						return rc;
				}
			}

			// The key already matches in all other cases
			if (op == MDB_SET_RANGE || op == MDB_SET_KEY)
				MDB_GET_KEY(leaf, key);
			DPRINTF(("==> cursor placed on key [%s]", DKEY(key)));

			return rc;
	*/

	return nil, false
}

// Move the cursor to the first item in the database.
func (c *cursor) first(key []byte, data []byte) error {
	/*
		int		 rc;
		MDB_node	*leaf;

		if (mc->mc_xcursor)
			mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);

		if (!(mc->mc_flags & C_INITIALIZED) || mc->mc_top) {
			rc = mdb_page_search(mc, NULL, MDB_PS_FIRST);
			if (rc != MDB_SUCCESS)
				return rc;
		}
		mdb_cassert(mc, IS_LEAF(mc->mc_pg[mc->mc_top]));

		leaf = NODEPTR(mc->mc_pg[mc->mc_top], 0);
		mc->mc_flags |= C_INITIALIZED;
		mc->mc_flags &= ~C_EOF;

		mc->mc_ki[mc->mc_top] = 0;

		if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
			key->mv_size = mc->mc_db->md_pad;
			key->mv_data = LEAF2KEY(mc->mc_pg[mc->mc_top], 0, key->mv_size);
			return MDB_SUCCESS;
		}

		if (data) {
			if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
				mdb_xcursor_init1(mc, leaf);
				rc = mdb_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
				if (rc)
					return rc;
			} else {
				if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
					return rc;
			}
		}
		MDB_GET_KEY(leaf, key);
		return MDB_SUCCESS;
	*/
	return nil
}

// Move the cursor to the last item in the database.
func (c *cursor) last() ([]byte, []byte) {
	/*
		int		 rc;
		MDB_node	*leaf;

		if (mc->mc_xcursor)
			mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);

		if (!(mc->mc_flags & C_EOF)) {

			if (!(mc->mc_flags & C_INITIALIZED) || mc->mc_top) {
				rc = mdb_page_search(mc, NULL, MDB_PS_LAST);
				if (rc != MDB_SUCCESS)
					return rc;
			}
			mdb_cassert(mc, IS_LEAF(mc->mc_pg[mc->mc_top]));

		}
		mc->mc_ki[mc->mc_top] = NUMKEYS(mc->mc_pg[mc->mc_top]) - 1;
		mc->mc_flags |= C_INITIALIZED|C_EOF;
		leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);

		if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
			key->mv_size = mc->mc_db->md_pad;
			key->mv_data = LEAF2KEY(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], key->mv_size);
			return MDB_SUCCESS;
		}

		if (data) {
			if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
				mdb_xcursor_init1(mc, leaf);
				rc = mdb_cursor_last(&mc->mc_xcursor->mx_cursor, data, NULL);
				if (rc)
					return rc;
			} else {
				if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
					return rc;
			}
		}

		MDB_GET_KEY(leaf, key);
		return MDB_SUCCESS;
	*/
	return nil, nil
}

func (c *cursor) Get(key []byte, data []byte, op int) ([]byte, []byte, error) {
	/*
			int		 rc;
			int		 exact = 0;
			int		 (*mfunc)(MDB_cursor *mc, MDB_val *key, MDB_val *data);

			if (mc == NULL)
				return EINVAL;

			if (mc->mc_txn->mt_flags & MDB_TXN_ERROR)
				return MDB_BAD_TXN;

			switch (op) {
			case MDB_GET_CURRENT:
				if (!(mc->mc_flags & C_INITIALIZED)) {
					rc = EINVAL;
				} else {
					MDB_page *mp = mc->mc_pg[mc->mc_top];
					int nkeys = NUMKEYS(mp);
					if (!nkeys || mc->mc_ki[mc->mc_top] >= nkeys) {
						mc->mc_ki[mc->mc_top] = nkeys;
						rc = MDB_NOTFOUND;
						break;
					}
					rc = MDB_SUCCESS;
					if (IS_LEAF2(mp)) {
						key->mv_size = mc->mc_db->md_pad;
						key->mv_data = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->mv_size);
					} else {
						MDB_node *leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
						MDB_GET_KEY(leaf, key);
						if (data) {
							if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
								if (mc->mc_flags & C_DEL)
									mdb_xcursor_init1(mc, leaf);
								rc = mdb_cursor_get(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_GET_CURRENT);
							} else {
								rc = mdb_node_read(mc->mc_txn, leaf, data);
							}
						}
					}
				}
				break;
			case MDB_GET_BOTH:
			case MDB_GET_BOTH_RANGE:
				if (data == NULL) {
					rc = EINVAL;
					break;
				}
				if (mc->mc_xcursor == NULL) {
					rc = MDB_INCOMPATIBLE;
					break;
				}
				// FALLTHRU
			case MDB_SET:
			case MDB_SET_KEY:
			case MDB_SET_RANGE:
				if (key == NULL) {
					rc = EINVAL;
				} else {
					rc = mdb_cursor_set(mc, key, data, op,
						op == MDB_SET_RANGE ? NULL : &exact);
				}
				break;
			case MDB_GET_MULTIPLE:
				if (data == NULL || !(mc->mc_flags & C_INITIALIZED)) {
					rc = EINVAL;
					break;
				}
				if (!(mc->mc_db->md_flags & MDB_DUPFIXED)) {
					rc = MDB_INCOMPATIBLE;
					break;
				}
				rc = MDB_SUCCESS;
				if (!(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) ||
					(mc->mc_xcursor->mx_cursor.mc_flags & C_EOF))
					break;
				goto fetchm;
			case MDB_NEXT_MULTIPLE:
				if (data == NULL) {
					rc = EINVAL;
					break;
				}
				if (!(mc->mc_db->md_flags & MDB_DUPFIXED)) {
					rc = MDB_INCOMPATIBLE;
					break;
				}
				if (!(mc->mc_flags & C_INITIALIZED))
					rc = mdb_cursor_first(mc, key, data);
				else
					rc = mdb_cursor_next(mc, key, data, MDB_NEXT_DUP);
				if (rc == MDB_SUCCESS) {
					if (mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) {
						MDB_cursor *mx;
		fetchm:
						mx = &mc->mc_xcursor->mx_cursor;
						data->mv_size = NUMKEYS(mx->mc_pg[mx->mc_top]) *
							mx->mc_db->md_pad;
						data->mv_data = METADATA(mx->mc_pg[mx->mc_top]);
						mx->mc_ki[mx->mc_top] = NUMKEYS(mx->mc_pg[mx->mc_top])-1;
					} else {
						rc = MDB_NOTFOUND;
					}
				}
				break;
			case MDB_NEXT:
			case MDB_NEXT_DUP:
			case MDB_NEXT_NODUP:
				if (!(mc->mc_flags & C_INITIALIZED))
					rc = mdb_cursor_first(mc, key, data);
				else
					rc = mdb_cursor_next(mc, key, data, op);
				break;
			case MDB_PREV:
			case MDB_PREV_DUP:
			case MDB_PREV_NODUP:
				if (!(mc->mc_flags & C_INITIALIZED)) {
					rc = mdb_cursor_last(mc, key, data);
					if (rc)
						break;
					mc->mc_flags |= C_INITIALIZED;
					mc->mc_ki[mc->mc_top]++;
				}
				rc = mdb_cursor_prev(mc, key, data, op);
				break;
			case MDB_FIRST:
				rc = mdb_cursor_first(mc, key, data);
				break;
			case MDB_FIRST_DUP:
				mfunc = mdb_cursor_first;
			mmove:
				if (data == NULL || !(mc->mc_flags & C_INITIALIZED)) {
					rc = EINVAL;
					break;
				}
				if (mc->mc_xcursor == NULL) {
					rc = MDB_INCOMPATIBLE;
					break;
				}
				if (!(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED)) {
					rc = EINVAL;
					break;
				}
				rc = mfunc(&mc->mc_xcursor->mx_cursor, data, NULL);
				break;
			case MDB_LAST:
				rc = mdb_cursor_last(mc, key, data);
				break;
			case MDB_LAST_DUP:
				mfunc = mdb_cursor_last;
				goto mmove;
			default:
				DPRINTF(("unhandled/unimplemented cursor operation %u", op));
				rc = EINVAL;
				break;
			}

			if (mc->mc_flags & C_DEL)
				mc->mc_flags ^= C_DEL;

			return rc;
	*/
	return nil, nil, nil
}

// Touch all the pages in the cursor stack. Set mc_top.
//	Makes sure all the pages are writable, before attempting a write operation.
// @param[in] mc The cursor to operate on.
func (c *cursor) touch() error {
	/*
			int rc = MDB_SUCCESS;

			if (mc->mc_dbi > MAIN_DBI && !(*mc->mc_dbflag & DB_DIRTY)) {
				MDB_cursor mc2;
				MDB_xcursor mcx;
				mdb_cursor_init(&mc2, mc->mc_txn, MAIN_DBI, &mcx);
				rc = mdb_page_search(&mc2, &mc->mc_dbx->md_name, MDB_PS_MODIFY);
				if (rc)
					 return rc;
				*mc->mc_dbflag |= DB_DIRTY;
			}
			mc->mc_top = 0;
			if (mc->mc_snum) {
				do {
					rc = mdb_page_touch(mc);
				} while (!rc && ++(mc->mc_top) < mc->mc_snum);
				mc->mc_top = mc->mc_snum-1;
			}
			return rc;
		}

		int
		mdb_cursor_put(MDB_cursor *mc, MDB_val *key, MDB_val *data,
		    unsigned int flags)
		{
			enum { MDB_NO_ROOT = MDB_LAST_ERRCODE+10 }; // internal code
			MDB_env		*env;
			MDB_node	*leaf = NULL;
			MDB_page	*fp, *mp;
			uint16_t	fp_flags;
			MDB_val		xdata, *rdata, dkey, olddata;
			MDB_db dummy;
			int do_sub = 0, insert;
			unsigned int mcount = 0, dcount = 0, nospill;
			size_t nsize;
			int rc, rc2;
			unsigned int nflags;
			DKBUF;

			if (mc == NULL || key == NULL)
				return EINVAL;

			env = mc->mc_txn->mt_env;

			// Check this first so counter will always be zero on any
			// early failures.
			if (flags & MDB_MULTIPLE) {
				dcount = data[1].mv_size;
				data[1].mv_size = 0;
				if (!F_ISSET(mc->mc_db->md_flags, MDB_DUPFIXED))
					return MDB_INCOMPATIBLE;
			}

			nospill = flags & MDB_NOSPILL;
			flags &= ~MDB_NOSPILL;

			if (mc->mc_txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_ERROR))
				return (mc->mc_txn->mt_flags & MDB_TXN_RDONLY) ? EACCES : MDB_BAD_TXN;

			if (flags != MDB_CURRENT && key->mv_size-1 >= ENV_MAXKEY(env))
				return MDB_BAD_VALSIZE;

		#if SIZE_MAX > MAXDATASIZE
			if (data->mv_size > ((mc->mc_db->md_flags & MDB_DUPSORT) ? ENV_MAXKEY(env) : MAXDATASIZE))
				return MDB_BAD_VALSIZE;
		#else
			if ((mc->mc_db->md_flags & MDB_DUPSORT) && data->mv_size > ENV_MAXKEY(env))
				return MDB_BAD_VALSIZE;
		#endif

			DPRINTF(("==> put db %d key [%s], size %"Z"u, data size %"Z"u",
				DDBI(mc), DKEY(key), key ? key->mv_size : 0, data->mv_size));

			dkey.mv_size = 0;

			if (flags == MDB_CURRENT) {
				if (!(mc->mc_flags & C_INITIALIZED))
					return EINVAL;
				rc = MDB_SUCCESS;
			} else if (mc->mc_db->md_root == P_INVALID) {
				// new database, cursor has nothing to point to
				mc->mc_snum = 0;
				mc->mc_top = 0;
				mc->mc_flags &= ~C_INITIALIZED;
				rc = MDB_NO_ROOT;
			} else {
				int exact = 0;
				MDB_val d2;
				if (flags & MDB_APPEND) {
					MDB_val k2;
					rc = mdb_cursor_last(mc, &k2, &d2);
					if (rc == 0) {
						rc = mc->mc_dbx->md_cmp(key, &k2);
						if (rc > 0) {
							rc = MDB_NOTFOUND;
							mc->mc_ki[mc->mc_top]++;
						} else {
							// new key is <= last key
							rc = MDB_KEYEXIST;
						}
					}
				} else {
					rc = mdb_cursor_set(mc, key, &d2, MDB_SET, &exact);
				}
				if ((flags & MDB_NOOVERWRITE) && rc == 0) {
					DPRINTF(("duplicate key [%s]", DKEY(key)));
					*data = d2;
					return MDB_KEYEXIST;
				}
				if (rc && rc != MDB_NOTFOUND)
					return rc;
			}

			if (mc->mc_flags & C_DEL)
				mc->mc_flags ^= C_DEL;

			// Cursor is positioned, check for room in the dirty list
			if (!nospill) {
				if (flags & MDB_MULTIPLE) {
					rdata = &xdata;
					xdata.mv_size = data->mv_size * dcount;
				} else {
					rdata = data;
				}
				if ((rc2 = mdb_page_spill(mc, key, rdata)))
					return rc2;
			}

			if (rc == MDB_NO_ROOT) {
				MDB_page *np;
				// new database, write a root leaf page
				DPUTS("allocating new root leaf page");
				if ((rc2 = mdb_page_new(mc, P_LEAF, 1, &np))) {
					return rc2;
				}
				mdb_cursor_push(mc, np);
				mc->mc_db->md_root = np->mp_pgno;
				mc->mc_db->md_depth++;
				*mc->mc_dbflag |= DB_DIRTY;
				if ((mc->mc_db->md_flags & (MDB_DUPSORT|MDB_DUPFIXED))
					== MDB_DUPFIXED)
					np->mp_flags |= P_LEAF2;
				mc->mc_flags |= C_INITIALIZED;
			} else {
				// make sure all cursor pages are writable
				rc2 = mdb_cursor_touch(mc);
				if (rc2)
					return rc2;
			}

			insert = rc;
			if (insert) {
				// The key does not exist
				DPRINTF(("inserting key at index %i", mc->mc_ki[mc->mc_top]));
				if ((mc->mc_db->md_flags & MDB_DUPSORT) &&
					LEAFSIZE(key, data) > env->me_nodemax)
				{
					// Too big for a node, insert in sub-DB
					fp_flags = P_LEAF|P_DIRTY;
					fp = env->me_pbuf;
					fp->mp_pad = data->mv_size; // used if MDB_DUPFIXED
					fp->mp_lower = fp->mp_upper = olddata.mv_size = PAGEHDRSZ;
					goto prep_subDB;
				}
			} else {
				// there's only a key anyway, so this is a no-op
				if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
					unsigned int ksize = mc->mc_db->md_pad;
					if (key->mv_size != ksize)
						return MDB_BAD_VALSIZE;
					if (flags == MDB_CURRENT) {
						char *ptr = LEAF2KEY(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], ksize);
						memcpy(ptr, key->mv_data, ksize);
					}
					return MDB_SUCCESS;
				}

		more:
				leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
				olddata.mv_size = NODEDSZ(leaf);
				olddata.mv_data = NODEDATA(leaf);

				// DB has dups?
				if (F_ISSET(mc->mc_db->md_flags, MDB_DUPSORT)) {
					// Prepare (sub-)page/sub-DB to accept the new item,
					// if needed.  fp: old sub-page or a header faking
					// it.  mp: new (sub-)page.  offset: growth in page
					// size.  xdata: node data with new page or DB.
					ssize_t		i, offset = 0;
					mp = fp = xdata.mv_data = env->me_pbuf;
					mp->mp_pgno = mc->mc_pg[mc->mc_top]->mp_pgno;

					// Was a single item before, must convert now
					if (!F_ISSET(leaf->mn_flags, F_DUPDATA)) {
						// Just overwrite the current item
						if (flags == MDB_CURRENT)
							goto current;

		#if UINT_MAX < SIZE_MAX
						if (mc->mc_dbx->md_dcmp == mdb_cmp_int && olddata.mv_size == sizeof(size_t))
		#ifdef MISALIGNED_OK
							mc->mc_dbx->md_dcmp = mdb_cmp_long;
		#else
							mc->mc_dbx->md_dcmp = mdb_cmp_cint;
		#endif
		#endif
						// if data matches, skip it
						if (!mc->mc_dbx->md_dcmp(data, &olddata)) {
							if (flags & MDB_NODUPDATA)
								rc = MDB_KEYEXIST;
							else if (flags & MDB_MULTIPLE)
								goto next_mult;
							else
								rc = MDB_SUCCESS;
							return rc;
						}

						// Back up original data item
						dkey.mv_size = olddata.mv_size;
						dkey.mv_data = memcpy(fp+1, olddata.mv_data, olddata.mv_size);

						// Make sub-page header for the dup items, with dummy body
						fp->mp_flags = P_LEAF|P_DIRTY|P_SUBP;
						fp->mp_lower = PAGEHDRSZ;
						xdata.mv_size = PAGEHDRSZ + dkey.mv_size + data->mv_size;
						if (mc->mc_db->md_flags & MDB_DUPFIXED) {
							fp->mp_flags |= P_LEAF2;
							fp->mp_pad = data->mv_size;
							xdata.mv_size += 2 * data->mv_size;	// leave space for 2 more
						} else {
							xdata.mv_size += 2 * (sizeof(indx_t) + NODESIZE) +
								(dkey.mv_size & 1) + (data->mv_size & 1);
						}
						fp->mp_upper = xdata.mv_size;
						olddata.mv_size = fp->mp_upper; // pretend olddata is fp
					} else if (leaf->mn_flags & F_SUBDATA) {
						// Data is on sub-DB, just store it
						flags |= F_DUPDATA|F_SUBDATA;
						goto put_sub;
					} else {
						// Data is on sub-page
						fp = olddata.mv_data;
						switch (flags) {
						default:
							i = -(ssize_t)SIZELEFT(fp);
							if (!(mc->mc_db->md_flags & MDB_DUPFIXED)) {
								offset = i += (ssize_t) EVEN(
									sizeof(indx_t) + NODESIZE + data->mv_size);
							} else {
								i += offset = fp->mp_pad;
								offset *= 4; // space for 4 more
							}
							if (i > 0)
								break;
							// FALLTHRU: Sub-page is big enough
						case MDB_CURRENT:
							fp->mp_flags |= P_DIRTY;
							COPY_PGNO(fp->mp_pgno, mp->mp_pgno);
							mc->mc_xcursor->mx_cursor.mc_pg[0] = fp;
							flags |= F_DUPDATA;
							goto put_sub;
						}
						xdata.mv_size = olddata.mv_size + offset;
					}

					fp_flags = fp->mp_flags;
					if (NODESIZE + NODEKSZ(leaf) + xdata.mv_size > env->me_nodemax) {
							// Too big for a sub-page, convert to sub-DB
							fp_flags &= ~P_SUBP;
		prep_subDB:
							if (mc->mc_db->md_flags & MDB_DUPFIXED) {
								fp_flags |= P_LEAF2;
								dummy.md_pad = fp->mp_pad;
								dummy.md_flags = MDB_DUPFIXED;
								if (mc->mc_db->md_flags & MDB_INTEGERDUP)
									dummy.md_flags |= MDB_INTEGERKEY;
							} else {
								dummy.md_pad = 0;
								dummy.md_flags = 0;
							}
							dummy.md_depth = 1;
							dummy.md_branch_pages = 0;
							dummy.md_leaf_pages = 1;
							dummy.md_overflow_pages = 0;
							dummy.md_entries = NUMKEYS(fp);
							xdata.mv_size = sizeof(MDB_db);
							xdata.mv_data = &dummy;
							if ((rc = mdb_page_alloc(mc, 1, &mp)))
								return rc;
							offset = env->me_psize - olddata.mv_size;
							flags |= F_DUPDATA|F_SUBDATA;
							dummy.md_root = mp->mp_pgno;
					}
					if (mp != fp) {
						mp->mp_flags = fp_flags | P_DIRTY;
						mp->mp_pad   = fp->mp_pad;
						mp->mp_lower = fp->mp_lower;
						mp->mp_upper = fp->mp_upper + offset;
						if (fp_flags & P_LEAF2) {
							memcpy(METADATA(mp), METADATA(fp), NUMKEYS(fp) * fp->mp_pad);
						} else {
							memcpy((char *)mp + mp->mp_upper, (char *)fp + fp->mp_upper,
								olddata.mv_size - fp->mp_upper);
							for (i = NUMKEYS(fp); --i >= 0; )
								mp->mp_ptrs[i] = fp->mp_ptrs[i] + offset;
						}
					}

					rdata = &xdata;
					flags |= F_DUPDATA;
					do_sub = 1;
					if (!insert)
						mdb_node_del(mc, 0);
					goto new_sub;
				}
		current:
				// overflow page overwrites need special handling
				if (F_ISSET(leaf->mn_flags, F_BIGDATA)) {
					MDB_page *omp;
					pgno_t pg;
					int level, ovpages, dpages = OVPAGES(data->mv_size, env->me_psize);

					memcpy(&pg, olddata.mv_data, sizeof(pg));
					if ((rc2 = mdb_page_get(mc->mc_txn, pg, &omp, &level)) != 0)
						return rc2;
					ovpages = omp->mp_pages;

					// Is the ov page large enough? 
					if (ovpages >= dpages) {
					  if (!(omp->mp_flags & P_DIRTY) &&
						  (level || (env->me_flags & MDB_WRITEMAP)))
					  {
						rc = mdb_page_unspill(mc->mc_txn, omp, &omp);
						if (rc)
							return rc;
						level = 0;		// dirty in this txn or clean 
					  }
					  // Is it dirty?
					  if (omp->mp_flags & P_DIRTY) {
						// yes, overwrite it. Note in this case we don't
						// bother to try shrinking the page if the new data
						// is smaller than the overflow threshold.
						if (level > 1) {
							// It is writable only in a parent txn
							size_t sz = (size_t) env->me_psize * ovpages, off;
							MDB_page *np = mdb_page_malloc(mc->mc_txn, ovpages);
							MDB_ID2 id2;
							if (!np)
								return ENOMEM;
							id2.mid = pg;
							id2.mptr = np;
							rc = mdb_mid2l_insert(mc->mc_txn->mt_u.dirty_list, &id2);
							mdb_cassert(mc, rc == 0);
							if (!(flags & MDB_RESERVE)) {
								// Copy end of page, adjusting alignment so
								// compiler may copy words instead of bytes.
								off = (PAGEHDRSZ + data->mv_size) & -sizeof(size_t);
								memcpy((size_t *)((char *)np + off),
									(size_t *)((char *)omp + off), sz - off);
								sz = PAGEHDRSZ;
							}
							memcpy(np, omp, sz); // Copy beginning of page
							omp = np;
						}
						SETDSZ(leaf, data->mv_size);
						if (F_ISSET(flags, MDB_RESERVE))
							data->mv_data = METADATA(omp);
						else
							memcpy(METADATA(omp), data->mv_data, data->mv_size);
						goto done;
					  }
					}
					if ((rc2 = mdb_ovpage_free(mc, omp)) != MDB_SUCCESS)
						return rc2;
				} else if (data->mv_size == olddata.mv_size) {
					// same size, just replace it. Note that we could
					// also reuse this node if the new data is smaller,
					// but instead we opt to shrink the node in that case.
					if (F_ISSET(flags, MDB_RESERVE))
						data->mv_data = olddata.mv_data;
					else if (data->mv_size)
						memcpy(olddata.mv_data, data->mv_data, data->mv_size);
					else
						memcpy(NODEKEY(leaf), key->mv_data, key->mv_size);
					goto done;
				}
				mdb_node_del(mc, 0);
				mc->mc_db->md_entries--;
			}

			rdata = data;

		new_sub:
			nflags = flags & NODE_ADD_FLAGS;
			nsize = IS_LEAF2(mc->mc_pg[mc->mc_top]) ? key->mv_size : mdb_leaf_size(env, key, rdata);
			if (SIZELEFT(mc->mc_pg[mc->mc_top]) < nsize) {
				if (( flags & (F_DUPDATA|F_SUBDATA)) == F_DUPDATA )
					nflags &= ~MDB_APPEND;
				if (!insert)
					nflags |= MDB_SPLIT_REPLACE;
				rc = mdb_page_split(mc, key, rdata, P_INVALID, nflags);
			} else {
				// There is room already in this leaf page.
				rc = mdb_node_add(mc, mc->mc_ki[mc->mc_top], key, rdata, 0, nflags);
				if (rc == 0 && !do_sub && insert) {
					// Adjust other cursors pointing to mp
					MDB_cursor *m2, *m3;
					MDB_dbi dbi = mc->mc_dbi;
					unsigned i = mc->mc_top;
					MDB_page *mp = mc->mc_pg[i];

					for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
						if (mc->mc_flags & C_SUB)
							m3 = &m2->mc_xcursor->mx_cursor;
						else
							m3 = m2;
						if (m3 == mc || m3->mc_snum < mc->mc_snum) continue;
						if (m3->mc_pg[i] == mp && m3->mc_ki[i] >= mc->mc_ki[i]) {
							m3->mc_ki[i]++;
						}
					}
				}
			}

			if (rc != MDB_SUCCESS)
				mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
			else {
				// Now store the actual data in the child DB. Note that we're
				// storing the user data in the keys field, so there are strict
				// size limits on dupdata. The actual data fields of the child
				// DB are all zero size.
				if (do_sub) {
					int xflags;
		put_sub:
					xdata.mv_size = 0;
					xdata.mv_data = "";
					leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
					if (flags & MDB_CURRENT) {
						xflags = MDB_CURRENT|MDB_NOSPILL;
					} else {
						mdb_xcursor_init1(mc, leaf);
						xflags = (flags & MDB_NODUPDATA) ?
							MDB_NOOVERWRITE|MDB_NOSPILL : MDB_NOSPILL;
					}
					// converted, write the original data first
					if (dkey.mv_size) {
						rc = mdb_cursor_put(&mc->mc_xcursor->mx_cursor, &dkey, &xdata, xflags);
						if (rc)
							return rc;
						{
							// Adjust other cursors pointing to mp
							MDB_cursor *m2;
							unsigned i = mc->mc_top;
							MDB_page *mp = mc->mc_pg[i];

							for (m2 = mc->mc_txn->mt_cursors[mc->mc_dbi]; m2; m2=m2->mc_next) {
								if (m2 == mc || m2->mc_snum < mc->mc_snum) continue;
								if (!(m2->mc_flags & C_INITIALIZED)) continue;
								if (m2->mc_pg[i] == mp && m2->mc_ki[i] == mc->mc_ki[i]) {
									mdb_xcursor_init1(m2, leaf);
								}
							}
						}
						// we've done our job
						dkey.mv_size = 0;
					}
					if (flags & MDB_APPENDDUP)
						xflags |= MDB_APPEND;
					rc = mdb_cursor_put(&mc->mc_xcursor->mx_cursor, data, &xdata, xflags);
					if (flags & F_SUBDATA) {
						void *db = NODEDATA(leaf);
						memcpy(db, &mc->mc_xcursor->mx_db, sizeof(MDB_db));
					}
				}
				// sub-writes might have failed so check rc again.
				// Don't increment count if we just replaced an existing item.
				if (!rc && !(flags & MDB_CURRENT))
					mc->mc_db->md_entries++;
				if (flags & MDB_MULTIPLE) {
					if (!rc) {
		next_mult:
						mcount++;
						// let caller know how many succeeded, if any
						data[1].mv_size = mcount;
						if (mcount < dcount) {
							data[0].mv_data = (char *)data[0].mv_data + data[0].mv_size;
							goto more;
						}
					}
				}
			}
		done:
			// If we succeeded and the key didn't exist before, make sure
			// the cursor is marked valid.
			if (!rc && insert)
				mc->mc_flags |= C_INITIALIZED;
			return rc;
	*/
	return nil
}

func (c *cursor) Del(flags int) error {
	/*
		MDB_node	*leaf;
		MDB_page	*mp;
		int rc;

		if (mc->mc_txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_ERROR))
			return (mc->mc_txn->mt_flags & MDB_TXN_RDONLY) ? EACCES : MDB_BAD_TXN;

		if (!(mc->mc_flags & C_INITIALIZED))
			return EINVAL;

		if (mc->mc_ki[mc->mc_top] >= NUMKEYS(mc->mc_pg[mc->mc_top]))
			return MDB_NOTFOUND;

		if (!(flags & MDB_NOSPILL) && (rc = mdb_page_spill(mc, NULL, NULL)))
			return rc;

		rc = mdb_cursor_touch(mc);
		if (rc)
			return rc;

		mp = mc->mc_pg[mc->mc_top];
		leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);

		if (!IS_LEAF2(mp) && F_ISSET(leaf->mn_flags, F_DUPDATA)) {
			if (!(flags & MDB_NODUPDATA)) {
				if (!F_ISSET(leaf->mn_flags, F_SUBDATA)) {
					mc->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(leaf);
				}
				rc = mdb_cursor_del(&mc->mc_xcursor->mx_cursor, MDB_NOSPILL);
				// If sub-DB still has entries, we're done
				if (mc->mc_xcursor->mx_db.md_entries) {
					if (leaf->mn_flags & F_SUBDATA) {
						// update subDB info
						void *db = NODEDATA(leaf);
						memcpy(db, &mc->mc_xcursor->mx_db, sizeof(MDB_db));
					} else {
						MDB_cursor *m2;
						// shrink fake page
						mdb_node_shrink(mp, mc->mc_ki[mc->mc_top]);
						leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
						mc->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(leaf);
						// fix other sub-DB cursors pointed at this fake page
						for (m2 = mc->mc_txn->mt_cursors[mc->mc_dbi]; m2; m2=m2->mc_next) {
							if (m2 == mc || m2->mc_snum < mc->mc_snum) continue;
							if (m2->mc_pg[mc->mc_top] == mp &&
								m2->mc_ki[mc->mc_top] == mc->mc_ki[mc->mc_top])
								m2->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(leaf);
						}
					}
					mc->mc_db->md_entries--;
					mc->mc_flags |= C_DEL;
					return rc;
				}
				// otherwise fall thru and delete the sub-DB
			}

			if (leaf->mn_flags & F_SUBDATA) {
				// add all the child DB's pages to the free list
				rc = mdb_drop0(&mc->mc_xcursor->mx_cursor, 0);
				if (rc == MDB_SUCCESS) {
					mc->mc_db->md_entries -=
						mc->mc_xcursor->mx_db.md_entries;
				}
			}
		}

		return mdb_cursor_del0(mc, leaf);
	*/
	return nil
}

// Allocate and initialize new pages for a database.
// @param[in] mc a cursor on the database being added to.
// @param[in] flags flags defining what type of page is being allocated.
// @param[in] num the number of pages to allocate. This is usually 1,
// unless allocating overflow pages for a large record.
// @param[out] mp Address of a page, or NULL on failure.
// @return 0 on success, non-zero on failure.
func (c *cursor) newPage(flags int, num int) ([]*page, error) {
	/*
		MDB_page	*np;
		int rc;

		if ((rc = mdb_page_alloc(mc, num, &np)))
			return rc;
		DPRINTF(("allocated new mpage %"Z"u, page size %u",
		    np->mp_pgno, mc->mc_txn->mt_env->me_psize));
		np->mp_flags = flags | P_DIRTY;
		np->mp_lower = PAGEHDRSZ;
		np->mp_upper = mc->mc_txn->mt_env->me_psize;

		if (IS_BRANCH(np))
			mc->mc_db->md_branch_pages++;
		else if (IS_LEAF(np))
			mc->mc_db->md_leaf_pages++;
		else if (IS_OVERFLOW(np)) {
			mc->mc_db->md_overflow_pages += num;
			np->mp_pages = num;
		}
		*mp = np;

		return 0;
	*/
	return nil, nil
}

// Add a node to the page pointed to by the cursor.
// @param[in] mc The cursor for this operation.
// @param[in] indx The index on the page where the new node should be added.
// @param[in] key The key for the new node.
// @param[in] data The data for the new node, if any.
// @param[in] pgno The page number, if adding a branch node.
// @param[in] flags Flags for the node.
// @return 0 on success, non-zero on failure. Possible errors are:
// <ul>
//	<li>ENOMEM - failed to allocate overflow pages for the node.
//	<li>MDB_PAGE_FULL - there is insufficient room in the page. This error
//	should never happen since all callers already calculate the
//	page's free space before calling this function.
// </ul>
func (c *cursor) addNode(index int, key []byte, data []byte, pgno int, flags int) error {
	/*
			unsigned int	 i;
			size_t		 node_size = NODESIZE;
			ssize_t		 room;
			indx_t		 ofs;
			MDB_node	*node;
			MDB_page	*mp = mc->mc_pg[mc->mc_top];
			MDB_page	*ofp = NULL;		// overflow page
			DKBUF;

			mdb_cassert(mc, mp->mp_upper >= mp->mp_lower);

			DPRINTF(("add to %s %spage %"Z"u index %i, data size %"Z"u key size %"Z"u [%s]",
			    IS_LEAF(mp) ? "leaf" : "branch",
				IS_SUBP(mp) ? "sub-" : "",
				mdb_dbg_pgno(mp), indx, data ? data->mv_size : 0,
				key ? key->mv_size : 0, key ? DKEY(key) : "null"));

			if (IS_LEAF2(mp)) {
				// Move higher keys up one slot.
				int ksize = mc->mc_db->md_pad, dif;
				char *ptr = LEAF2KEY(mp, indx, ksize);
				dif = NUMKEYS(mp) - indx;
				if (dif > 0)
					memmove(ptr+ksize, ptr, dif*ksize);
				// insert new key
				memcpy(ptr, key->mv_data, ksize);

				// Just using these for counting
				mp->mp_lower += sizeof(indx_t);
				mp->mp_upper -= ksize - sizeof(indx_t);
				return MDB_SUCCESS;
			}

			room = (ssize_t)SIZELEFT(mp) - (ssize_t)sizeof(indx_t);
			if (key != NULL)
				node_size += key->mv_size;
			if (IS_LEAF(mp)) {
				mdb_cassert(mc, data);
				if (F_ISSET(flags, F_BIGDATA)) {
					// Data already on overflow page.
					node_size += sizeof(pgno_t);
				} else if (node_size + data->mv_size > mc->mc_txn->mt_env->me_nodemax) {
					int ovpages = OVPAGES(data->mv_size, mc->mc_txn->mt_env->me_psize);
					int rc;
					// Put data on overflow page.
					DPRINTF(("data size is %"Z"u, node would be %"Z"u, put data on overflow page",
					    data->mv_size, node_size+data->mv_size));
					node_size = EVEN(node_size + sizeof(pgno_t));
					if ((ssize_t)node_size > room)
						goto full;
					if ((rc = mdb_page_new(mc, P_OVERFLOW, ovpages, &ofp)))
						return rc;
					DPRINTF(("allocated overflow page %"Z"u", ofp->mp_pgno));
					flags |= F_BIGDATA;
					goto update;
				} else {
					node_size += data->mv_size;
				}
			}
			node_size = EVEN(node_size);
			if ((ssize_t)node_size > room)
				goto full;

		update:
			// Move higher pointers up one slot.
			for (i = NUMKEYS(mp); i > indx; i--)
				mp->mp_ptrs[i] = mp->mp_ptrs[i - 1];

			// Adjust free space offsets.
			ofs = mp->mp_upper - node_size;
			mdb_cassert(mc, ofs >= mp->mp_lower + sizeof(indx_t));
			mp->mp_ptrs[indx] = ofs;
			mp->mp_upper = ofs;
			mp->mp_lower += sizeof(indx_t);

			// Write the node data.
			node = NODEPTR(mp, indx);
			node->mn_ksize = (key == NULL) ? 0 : key->mv_size;
			node->mn_flags = flags;
			if (IS_LEAF(mp))
				SETDSZ(node,data->mv_size);
			else
				SETPGNO(node,pgno);

			if (key)
				memcpy(NODEKEY(node), key->mv_data, key->mv_size);

			if (IS_LEAF(mp)) {
				mdb_cassert(mc, key);
				if (ofp == NULL) {
					if (F_ISSET(flags, F_BIGDATA))
						memcpy(node->mn_data + key->mv_size, data->mv_data,
						    sizeof(pgno_t));
					else if (F_ISSET(flags, MDB_RESERVE))
						data->mv_data = node->mn_data + key->mv_size;
					else
						memcpy(node->mn_data + key->mv_size, data->mv_data,
						    data->mv_size);
				} else {
					memcpy(node->mn_data + key->mv_size, &ofp->mp_pgno,
					    sizeof(pgno_t));
					if (F_ISSET(flags, MDB_RESERVE))
						data->mv_data = METADATA(ofp);
					else
						memcpy(METADATA(ofp), data->mv_data, data->mv_size);
				}
			}

			return MDB_SUCCESS;

		full:
			DPRINTF(("not enough room in page %"Z"u, got %u ptrs",
				mdb_dbg_pgno(mp), NUMKEYS(mp)));
			DPRINTF(("upper-lower = %u - %u = %"Z"d", mp->mp_upper,mp->mp_lower,room));
			DPRINTF(("node size = %"Z"u", node_size));
			mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
			return MDB_PAGE_FULL;
	*/

	return nil
}

// Delete the specified node from a page.
// @param[in] mp The page to operate on.
// @param[in] indx The index of the node to delete.
// @param[in] ksize The size of a node. Only used if the page is
// part of a #MDB_DUPFIXED database.
func (c *cursor) deleteNode(ksize int) {
	/*
		MDB_page *mp = mc->mc_pg[mc->mc_top];
		indx_t	indx = mc->mc_ki[mc->mc_top];
		unsigned int	 sz;
		indx_t		 i, j, numkeys, ptr;
		MDB_node	*node;
		char		*base;

		DPRINTF(("delete node %u on %s page %"Z"u", indx,
		    IS_LEAF(mp) ? "leaf" : "branch", mdb_dbg_pgno(mp)));
		numkeys = NUMKEYS(mp);
		mdb_cassert(mc, indx < numkeys);

		if (IS_LEAF2(mp)) {
			int x = numkeys - 1 - indx;
			base = LEAF2KEY(mp, indx, ksize);
			if (x)
				memmove(base, base + ksize, x * ksize);
			mp->mp_lower -= sizeof(indx_t);
			mp->mp_upper += ksize - sizeof(indx_t);
			return;
		}

		node = NODEPTR(mp, indx);
		sz = NODESIZE + node->mn_ksize;
		if (IS_LEAF(mp)) {
			if (F_ISSET(node->mn_flags, F_BIGDATA))
				sz += sizeof(pgno_t);
			else
				sz += NODEDSZ(node);
		}
		sz = EVEN(sz);

		ptr = mp->mp_ptrs[indx];
		for (i = j = 0; i < numkeys; i++) {
			if (i != indx) {
				mp->mp_ptrs[j] = mp->mp_ptrs[i];
				if (mp->mp_ptrs[i] < ptr)
					mp->mp_ptrs[j] += sz;
				j++;
			}
		}

		base = (char *)mp + mp->mp_upper;
		memmove(base + sz, base, ptr - mp->mp_upper);

		mp->mp_lower -= sizeof(indx_t);
		mp->mp_upper += sz;
	*/
}

// Initial setup of a sorted-dups cursor.
// Sorted duplicates are implemented as a sub-database for the given key.
// The duplicate data items are actually keys of the sub-database.
// Operations on the duplicate data items are performed using a sub-cursor
// initialized when the sub-database is first accessed. This function does
// the preliminary setup of the sub-cursor, filling in the fields that
// depend only on the parent DB.
// @param[in] mc The main cursor whose sorted-dups cursor is to be initialized.
func (c *cursor) xcursor_init0() {
	/*
		MDB_xcursor *mx = mc->mc_xcursor;

		mx->mx_cursor.mc_xcursor = NULL;
		mx->mx_cursor.mc_txn = mc->mc_txn;
		mx->mx_cursor.mc_db = &mx->mx_db;
		mx->mx_cursor.mc_dbx = &mx->mx_dbx;
		mx->mx_cursor.mc_dbi = mc->mc_dbi;
		mx->mx_cursor.mc_dbflag = &mx->mx_dbflag;
		mx->mx_cursor.mc_snum = 0;
		mx->mx_cursor.mc_top = 0;
		mx->mx_cursor.mc_flags = C_SUB;
		mx->mx_dbx.md_name.mv_size = 0;
		mx->mx_dbx.md_name.mv_data = NULL;
		mx->mx_dbx.md_cmp = mc->mc_dbx->md_dcmp;
		mx->mx_dbx.md_dcmp = NULL;
		mx->mx_dbx.md_rel = mc->mc_dbx->md_rel;
	*/
}

// Final setup of a sorted-dups cursor.
//	Sets up the fields that depend on the data from the main cursor.
// @param[in] mc The main cursor whose sorted-dups cursor is to be initialized.
// @param[in] node The data containing the #MDB_db record for the
// sorted-dup database.
func (c *cursor) xcursor_init1(n *node) {
	/*
			MDB_xcursor *mx = mc->mc_xcursor;

			if (node->mn_flags & F_SUBDATA) {
				memcpy(&mx->mx_db, NODEDATA(node), sizeof(MDB_db));
				mx->mx_cursor.mc_pg[0] = 0;
				mx->mx_cursor.mc_snum = 0;
				mx->mx_cursor.mc_top = 0;
				mx->mx_cursor.mc_flags = C_SUB;
			} else {
				MDB_page *fp = NODEDATA(node);
				mx->mx_db.md_pad = mc->mc_pg[mc->mc_top]->mp_pad;
				mx->mx_db.md_flags = 0;
				mx->mx_db.md_depth = 1;
				mx->mx_db.md_branch_pages = 0;
				mx->mx_db.md_leaf_pages = 1;
				mx->mx_db.md_overflow_pages = 0;
				mx->mx_db.md_entries = NUMKEYS(fp);
				COPY_PGNO(mx->mx_db.md_root, fp->mp_pgno);
				mx->mx_cursor.mc_snum = 1;
				mx->mx_cursor.mc_top = 0;
				mx->mx_cursor.mc_flags = C_INITIALIZED|C_SUB;
				mx->mx_cursor.mc_pg[0] = fp;
				mx->mx_cursor.mc_ki[0] = 0;
				if (mc->mc_db->md_flags & MDB_DUPFIXED) {
					mx->mx_db.md_flags = MDB_DUPFIXED;
					mx->mx_db.md_pad = fp->mp_pad;
					if (mc->mc_db->md_flags & MDB_INTEGERDUP)
						mx->mx_db.md_flags |= MDB_INTEGERKEY;
				}
			}
			DPRINTF(("Sub-db -%u root page %"Z"u", mx->mx_cursor.mc_dbi,
				mx->mx_db.md_root));
			mx->mx_dbflag = DB_VALID|DB_DIRTY; // DB_DIRTY guides mdb_cursor_touch
		#if UINT_MAX < SIZE_MAX
			if (mx->mx_dbx.md_cmp == mdb_cmp_int && mx->mx_db.md_pad == sizeof(size_t))
		#ifdef MISALIGNED_OK
				mx->mx_dbx.md_cmp = mdb_cmp_long;
		#else
				mx->mx_dbx.md_cmp = mdb_cmp_cint;
		#endif
		#endif
	*/
}

// Initialize a cursor for a given transaction and database.
func (c *cursor) init(t *transaction, bucket *Bucket, mx *xcursor) {
	/*
		mc->mc_next = NULL;
		mc->mc_backup = NULL;
		mc->mc_dbi = dbi;
		mc->mc_txn = txn;
		mc->mc_db = &txn->mt_dbs[dbi];
		mc->mc_dbx = &txn->mt_dbxs[dbi];
		mc->mc_dbflag = &txn->mt_dbflags[dbi];
		mc->mc_snum = 0;
		mc->mc_top = 0;
		mc->mc_pg[0] = 0;
		mc->mc_flags = 0;
		if (txn->mt_dbs[dbi].md_flags & MDB_DUPSORT) {
			mdb_tassert(txn, mx != NULL);
			mc->mc_xcursor = mx;
			mdb_xcursor_init0(mc);
		} else {
			mc->mc_xcursor = NULL;
		}
		if (*mc->mc_dbflag & DB_STALE) {
			mdb_page_search(mc, NULL, MDB_PS_ROOTONLY);
		}
	*/
}

// Return the count of duplicate data items for the current key.
func (c *cursor) count() (int, error) {
	/*
		MDB_node	*leaf;

		if (mc == NULL || countp == NULL)
			return EINVAL;

		if (mc->mc_xcursor == NULL)
			return MDB_INCOMPATIBLE;

		leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
		if (!F_ISSET(leaf->mn_flags, F_DUPDATA)) {
			*countp = 1;
		} else {
			if (!(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED))
				return EINVAL;

			*countp = mc->mc_xcursor->mx_db.md_entries;
		}
		return MDB_SUCCESS;
	*/
	return 0, nil
}

func (c *cursor) Close() {
	/*
		if (mc && !mc->mc_backup) {
			// remove from txn, if tracked
			if ((mc->mc_flags & C_UNTRACK) && mc->mc_txn->mt_cursors) {
				MDB_cursor **prev = &mc->mc_txn->mt_cursors[mc->mc_dbi];
				while (*prev && *prev != mc) prev = &(*prev)->mc_next;
				if (*prev == mc)
					*prev = mc->mc_next;
			}
			free(mc);
		}
	*/
}

func (c *cursor) Transaction() Transaction {
	/*
		if (!mc) return NULL;
		return mc->mc_txn;
	*/
	return nil
}

func (c *cursor) Bucket() *Bucket {
	return c.bucket
}

// Replace the key for a branch node with a new key.
// @param[in] mc Cursor pointing to the node to operate on.
// @param[in] key The new key to use.
// @return 0 on success, non-zero on failure.
func (c *cursor) updateKey(key []byte) error {
	/*
			MDB_page		*mp;
			MDB_node		*node;
			char			*base;
			size_t			 len;
			int				 delta, ksize, oksize;
			indx_t			 ptr, i, numkeys, indx;
			DKBUF;

			indx = mc->mc_ki[mc->mc_top];
			mp = mc->mc_pg[mc->mc_top];
			node = NODEPTR(mp, indx);
			ptr = mp->mp_ptrs[indx];
		#if MDB_DEBUG
			{
				MDB_val	k2;
				char kbuf2[DKBUF_MAXKEYSIZE*2+1];
				k2.mv_data = NODEKEY(node);
				k2.mv_size = node->mn_ksize;
				DPRINTF(("update key %u (ofs %u) [%s] to [%s] on page %"Z"u",
					indx, ptr,
					mdb_dkey(&k2, kbuf2),
					DKEY(key),
					mp->mp_pgno));
			}
		#endif

			// Sizes must be 2-byte aligned.
			ksize = EVEN(key->mv_size);
			oksize = EVEN(node->mn_ksize);
			delta = ksize - oksize;

			// Shift node contents if EVEN(key length) changed.
			if (delta) {
				if (delta > 0 && SIZELEFT(mp) < delta) {
					pgno_t pgno;
					// not enough space left, do a delete and split
					DPRINTF(("Not enough room, delta = %d, splitting...", delta));
					pgno = NODEPGNO(node);
					mdb_node_del(mc, 0);
					return mdb_page_split(mc, key, NULL, pgno, MDB_SPLIT_REPLACE);
				}

				numkeys = NUMKEYS(mp);
				for (i = 0; i < numkeys; i++) {
					if (mp->mp_ptrs[i] <= ptr)
						mp->mp_ptrs[i] -= delta;
				}

				base = (char *)mp + mp->mp_upper;
				len = ptr - mp->mp_upper + NODESIZE;
				memmove(base - delta, base, len);
				mp->mp_upper -= delta;

				node = NODEPTR(mp, indx);
			}

			// But even if no shift was needed, update ksize
			if (node->mn_ksize != key->mv_size)
				node->mn_ksize = key->mv_size;

			if (key->mv_size)
				memcpy(NODEKEY(node), key->mv_data, key->mv_size);

			return MDB_SUCCESS;
	*/
	return nil
}

// Move a node from csrc to cdst.
func (c *cursor) moveNodeTo(dst *cursor) error {
	/*
		MDB_node		*srcnode;
		MDB_val		 key, data;
		pgno_t	srcpg;
		MDB_cursor mn;
		int			 rc;
		unsigned short flags;

		DKBUF;

		// Mark src and dst as dirty.
		if ((rc = mdb_page_touch(csrc)) ||
		    (rc = mdb_page_touch(cdst)))
			return rc;

		if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
			key.mv_size = csrc->mc_db->md_pad;
			key.mv_data = LEAF2KEY(csrc->mc_pg[csrc->mc_top], csrc->mc_ki[csrc->mc_top], key.mv_size);
			data.mv_size = 0;
			data.mv_data = NULL;
			srcpg = 0;
			flags = 0;
		} else {
			srcnode = NODEPTR(csrc->mc_pg[csrc->mc_top], csrc->mc_ki[csrc->mc_top]);
			mdb_cassert(csrc, !((size_t)srcnode & 1));
			srcpg = NODEPGNO(srcnode);
			flags = srcnode->mn_flags;
			if (csrc->mc_ki[csrc->mc_top] == 0 && IS_BRANCH(csrc->mc_pg[csrc->mc_top])) {
				unsigned int snum = csrc->mc_snum;
				MDB_node *s2;
				// must find the lowest key below src
				mdb_page_search_lowest(csrc);
				if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
					key.mv_size = csrc->mc_db->md_pad;
					key.mv_data = LEAF2KEY(csrc->mc_pg[csrc->mc_top], 0, key.mv_size);
				} else {
					s2 = NODEPTR(csrc->mc_pg[csrc->mc_top], 0);
					key.mv_size = NODEKSZ(s2);
					key.mv_data = NODEKEY(s2);
				}
				csrc->mc_snum = snum--;
				csrc->mc_top = snum;
			} else {
				key.mv_size = NODEKSZ(srcnode);
				key.mv_data = NODEKEY(srcnode);
			}
			data.mv_size = NODEDSZ(srcnode);
			data.mv_data = NODEDATA(srcnode);
		}
		if (IS_BRANCH(cdst->mc_pg[cdst->mc_top]) && cdst->mc_ki[cdst->mc_top] == 0) {
			unsigned int snum = cdst->mc_snum;
			MDB_node *s2;
			MDB_val bkey;
			// must find the lowest key below dst
			mdb_page_search_lowest(cdst);
			if (IS_LEAF2(cdst->mc_pg[cdst->mc_top])) {
				bkey.mv_size = cdst->mc_db->md_pad;
				bkey.mv_data = LEAF2KEY(cdst->mc_pg[cdst->mc_top], 0, bkey.mv_size);
			} else {
				s2 = NODEPTR(cdst->mc_pg[cdst->mc_top], 0);
				bkey.mv_size = NODEKSZ(s2);
				bkey.mv_data = NODEKEY(s2);
			}
			cdst->mc_snum = snum--;
			cdst->mc_top = snum;
			mdb_cursor_copy(cdst, &mn);
			mn.mc_ki[snum] = 0;
			rc = mdb_update_key(&mn, &bkey);
			if (rc)
				return rc;
		}

		DPRINTF(("moving %s node %u [%s] on page %"Z"u to node %u on page %"Z"u",
		    IS_LEAF(csrc->mc_pg[csrc->mc_top]) ? "leaf" : "branch",
		    csrc->mc_ki[csrc->mc_top],
			DKEY(&key),
		    csrc->mc_pg[csrc->mc_top]->mp_pgno,
		    cdst->mc_ki[cdst->mc_top], cdst->mc_pg[cdst->mc_top]->mp_pgno));

		// Add the node to the destination page.
		rc = mdb_node_add(cdst, cdst->mc_ki[cdst->mc_top], &key, &data, srcpg, flags);
		if (rc != MDB_SUCCESS)
			return rc;

		// Delete the node from the source page.
		mdb_node_del(csrc, key.mv_size);

		{
			// Adjust other cursors pointing to mp
			MDB_cursor *m2, *m3;
			MDB_dbi dbi = csrc->mc_dbi;
			MDB_page *mp = csrc->mc_pg[csrc->mc_top];

			for (m2 = csrc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
				if (csrc->mc_flags & C_SUB)
					m3 = &m2->mc_xcursor->mx_cursor;
				else
					m3 = m2;
				if (m3 == csrc) continue;
				if (m3->mc_pg[csrc->mc_top] == mp && m3->mc_ki[csrc->mc_top] ==
					csrc->mc_ki[csrc->mc_top]) {
					m3->mc_pg[csrc->mc_top] = cdst->mc_pg[cdst->mc_top];
					m3->mc_ki[csrc->mc_top] = cdst->mc_ki[cdst->mc_top];
				}
			}
		}

		// Update the parent separators.
		if (csrc->mc_ki[csrc->mc_top] == 0) {
			if (csrc->mc_ki[csrc->mc_top-1] != 0) {
				if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
					key.mv_data = LEAF2KEY(csrc->mc_pg[csrc->mc_top], 0, key.mv_size);
				} else {
					srcnode = NODEPTR(csrc->mc_pg[csrc->mc_top], 0);
					key.mv_size = NODEKSZ(srcnode);
					key.mv_data = NODEKEY(srcnode);
				}
				DPRINTF(("update separator for source page %"Z"u to [%s]",
					csrc->mc_pg[csrc->mc_top]->mp_pgno, DKEY(&key)));
				mdb_cursor_copy(csrc, &mn);
				mn.mc_snum--;
				mn.mc_top--;
				if ((rc = mdb_update_key(&mn, &key)) != MDB_SUCCESS)
					return rc;
			}
			if (IS_BRANCH(csrc->mc_pg[csrc->mc_top])) {
				MDB_val	 nullkey;
				indx_t	ix = csrc->mc_ki[csrc->mc_top];
				nullkey.mv_size = 0;
				csrc->mc_ki[csrc->mc_top] = 0;
				rc = mdb_update_key(csrc, &nullkey);
				csrc->mc_ki[csrc->mc_top] = ix;
				mdb_cassert(csrc, rc == MDB_SUCCESS);
			}
		}

		if (cdst->mc_ki[cdst->mc_top] == 0) {
			if (cdst->mc_ki[cdst->mc_top-1] != 0) {
				if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
					key.mv_data = LEAF2KEY(cdst->mc_pg[cdst->mc_top], 0, key.mv_size);
				} else {
					srcnode = NODEPTR(cdst->mc_pg[cdst->mc_top], 0);
					key.mv_size = NODEKSZ(srcnode);
					key.mv_data = NODEKEY(srcnode);
				}
				DPRINTF(("update separator for destination page %"Z"u to [%s]",
					cdst->mc_pg[cdst->mc_top]->mp_pgno, DKEY(&key)));
				mdb_cursor_copy(cdst, &mn);
				mn.mc_snum--;
				mn.mc_top--;
				if ((rc = mdb_update_key(&mn, &key)) != MDB_SUCCESS)
					return rc;
			}
			if (IS_BRANCH(cdst->mc_pg[cdst->mc_top])) {
				MDB_val	 nullkey;
				indx_t	ix = cdst->mc_ki[cdst->mc_top];
				nullkey.mv_size = 0;
				cdst->mc_ki[cdst->mc_top] = 0;
				rc = mdb_update_key(cdst, &nullkey);
				cdst->mc_ki[cdst->mc_top] = ix;
				mdb_cassert(csrc, rc == MDB_SUCCESS);
			}
		}

		return MDB_SUCCESS;
	*/

	return nil
}

// Merge one page into another.
//  The nodes from the page pointed to by \b csrc will
//	be copied to the page pointed to by \b cdst and then
//	the \b csrc page will be freed.
// @param[in] csrc Cursor pointing to the source page.
// @param[in] cdst Cursor pointing to the destination page.
func (c *cursor) mergePage(dst *cursor) error {
	/*
		int			 rc;
		indx_t			 i, j;
		MDB_node		*srcnode;
		MDB_val		 key, data;
		unsigned	nkeys;

		DPRINTF(("merging page %"Z"u into %"Z"u", csrc->mc_pg[csrc->mc_top]->mp_pgno,
			cdst->mc_pg[cdst->mc_top]->mp_pgno));

		mdb_cassert(csrc, csrc->mc_snum > 1);	// can't merge root page
		mdb_cassert(csrc, cdst->mc_snum > 1);

		// Mark dst as dirty.
		if ((rc = mdb_page_touch(cdst)))
			return rc;

		// Move all nodes from src to dst.
		j = nkeys = NUMKEYS(cdst->mc_pg[cdst->mc_top]);
		if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
			key.mv_size = csrc->mc_db->md_pad;
			key.mv_data = METADATA(csrc->mc_pg[csrc->mc_top]);
			for (i = 0; i < NUMKEYS(csrc->mc_pg[csrc->mc_top]); i++, j++) {
				rc = mdb_node_add(cdst, j, &key, NULL, 0, 0);
				if (rc != MDB_SUCCESS)
					return rc;
				key.mv_data = (char *)key.mv_data + key.mv_size;
			}
		} else {
			for (i = 0; i < NUMKEYS(csrc->mc_pg[csrc->mc_top]); i++, j++) {
				srcnode = NODEPTR(csrc->mc_pg[csrc->mc_top], i);
				if (i == 0 && IS_BRANCH(csrc->mc_pg[csrc->mc_top])) {
					unsigned int snum = csrc->mc_snum;
					MDB_node *s2;
					// must find the lowest key below src
					mdb_page_search_lowest(csrc);
					if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
						key.mv_size = csrc->mc_db->md_pad;
						key.mv_data = LEAF2KEY(csrc->mc_pg[csrc->mc_top], 0, key.mv_size);
					} else {
						s2 = NODEPTR(csrc->mc_pg[csrc->mc_top], 0);
						key.mv_size = NODEKSZ(s2);
						key.mv_data = NODEKEY(s2);
					}
					csrc->mc_snum = snum--;
					csrc->mc_top = snum;
				} else {
					key.mv_size = srcnode->mn_ksize;
					key.mv_data = NODEKEY(srcnode);
				}

				data.mv_size = NODEDSZ(srcnode);
				data.mv_data = NODEDATA(srcnode);
				rc = mdb_node_add(cdst, j, &key, &data, NODEPGNO(srcnode), srcnode->mn_flags);
				if (rc != MDB_SUCCESS)
					return rc;
			}
		}

		DPRINTF(("dst page %"Z"u now has %u keys (%.1f%% filled)",
		    cdst->mc_pg[cdst->mc_top]->mp_pgno, NUMKEYS(cdst->mc_pg[cdst->mc_top]),
			(float)PAGEFILL(cdst->mc_txn->mt_env, cdst->mc_pg[cdst->mc_top]) / 10));

		// Unlink the src page from parent and add to free list.
		csrc->mc_top--;
		mdb_node_del(csrc, 0);
		if (csrc->mc_ki[csrc->mc_top] == 0) {
			key.mv_size = 0;
			rc = mdb_update_key(csrc, &key);
			if (rc) {
				csrc->mc_top++;
				return rc;
			}
		}
		csrc->mc_top++;

		rc = mdb_midl_append(&csrc->mc_txn->mt_free_pgs,
			csrc->mc_pg[csrc->mc_top]->mp_pgno);
		if (rc)
			return rc;
		if (IS_LEAF(csrc->mc_pg[csrc->mc_top]))
			csrc->mc_db->md_leaf_pages--;
		else
			csrc->mc_db->md_branch_pages--;
		{
			// Adjust other cursors pointing to mp 
			MDB_cursor *m2, *m3;
			MDB_dbi dbi = csrc->mc_dbi;
			MDB_page *mp = cdst->mc_pg[cdst->mc_top];

			for (m2 = csrc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
				if (csrc->mc_flags & C_SUB)
					m3 = &m2->mc_xcursor->mx_cursor;
				else
					m3 = m2;
				if (m3 == csrc) continue;
				if (m3->mc_snum < csrc->mc_snum) continue;
				if (m3->mc_pg[csrc->mc_top] == csrc->mc_pg[csrc->mc_top]) {
					m3->mc_pg[csrc->mc_top] = mp;
					m3->mc_ki[csrc->mc_top] += nkeys;
				}
			}
		}
		mdb_cursor_pop(csrc);

		return mdb_rebalance(csrc);
	*/

	return nil
}

// Copy the contents of a cursor.
// @param[in] csrc The cursor to copy from.
// @param[out] cdst The cursor to copy to.
func (c *cursor) copyTo(dst *cursor) {
	/*
		unsigned int i;

		cdst->mc_txn = csrc->mc_txn;
		cdst->mc_dbi = csrc->mc_dbi;
		cdst->mc_db  = csrc->mc_db;
		cdst->mc_dbx = csrc->mc_dbx;
		cdst->mc_snum = csrc->mc_snum;
		cdst->mc_top = csrc->mc_top;
		cdst->mc_flags = csrc->mc_flags;

		for (i=0; i<csrc->mc_snum; i++) {
			cdst->mc_pg[i] = csrc->mc_pg[i];
			cdst->mc_ki[i] = csrc->mc_ki[i];
		}
	*/
}

// Rebalance the tree after a delete operation.
// @param[in] mc Cursor pointing to the page where rebalancing
// should begin.
// @return 0 on success, non-zero on failure.
func (c *cursor) rebalance() error {
	/*
		MDB_node	*node;
		int rc;
		unsigned int ptop, minkeys;
		MDB_cursor	mn;

		minkeys = 1 + (IS_BRANCH(mc->mc_pg[mc->mc_top]));
		DPRINTF(("rebalancing %s page %"Z"u (has %u keys, %.1f%% full)",
		    IS_LEAF(mc->mc_pg[mc->mc_top]) ? "leaf" : "branch",
		    mdb_dbg_pgno(mc->mc_pg[mc->mc_top]), NUMKEYS(mc->mc_pg[mc->mc_top]),
			(float)PAGEFILL(mc->mc_txn->mt_env, mc->mc_pg[mc->mc_top]) / 10));

		if (PAGEFILL(mc->mc_txn->mt_env, mc->mc_pg[mc->mc_top]) >= FILL_THRESHOLD &&
			NUMKEYS(mc->mc_pg[mc->mc_top]) >= minkeys) {
			DPRINTF(("no need to rebalance page %"Z"u, above fill threshold",
			    mdb_dbg_pgno(mc->mc_pg[mc->mc_top])));
			return MDB_SUCCESS;
		}

		if (mc->mc_snum < 2) {
			MDB_page *mp = mc->mc_pg[0];
			if (IS_SUBP(mp)) {
				DPUTS("Can't rebalance a subpage, ignoring");
				return MDB_SUCCESS;
			}
			if (NUMKEYS(mp) == 0) {
				DPUTS("tree is completely empty");
				mc->mc_db->md_root = P_INVALID;
				mc->mc_db->md_depth = 0;
				mc->mc_db->md_leaf_pages = 0;
				rc = mdb_midl_append(&mc->mc_txn->mt_free_pgs, mp->mp_pgno);
				if (rc)
					return rc;
				// Adjust cursors pointing to mp
				mc->mc_snum = 0;
				mc->mc_top = 0;
				mc->mc_flags &= ~C_INITIALIZED;
				{
					MDB_cursor *m2, *m3;
					MDB_dbi dbi = mc->mc_dbi;

					for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
						if (mc->mc_flags & C_SUB)
							m3 = &m2->mc_xcursor->mx_cursor;
						else
							m3 = m2;
						if (m3->mc_snum < mc->mc_snum) continue;
						if (m3->mc_pg[0] == mp) {
							m3->mc_snum = 0;
							m3->mc_top = 0;
							m3->mc_flags &= ~C_INITIALIZED;
						}
					}
				}
			} else if (IS_BRANCH(mp) && NUMKEYS(mp) == 1) {
				DPUTS("collapsing root page!");
				rc = mdb_midl_append(&mc->mc_txn->mt_free_pgs, mp->mp_pgno);
				if (rc)
					return rc;
				mc->mc_db->md_root = NODEPGNO(NODEPTR(mp, 0));
				rc = mdb_page_get(mc->mc_txn,mc->mc_db->md_root,&mc->mc_pg[0],NULL);
				if (rc)
					return rc;
				mc->mc_db->md_depth--;
				mc->mc_db->md_branch_pages--;
				mc->mc_ki[0] = mc->mc_ki[1];
				{
					// Adjust other cursors pointing to mp
					MDB_cursor *m2, *m3;
					MDB_dbi dbi = mc->mc_dbi;

					for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
						if (mc->mc_flags & C_SUB)
							m3 = &m2->mc_xcursor->mx_cursor;
						else
							m3 = m2;
						if (m3 == mc || m3->mc_snum < mc->mc_snum) continue;
						if (m3->mc_pg[0] == mp) {
							int i;
							m3->mc_snum--;
							m3->mc_top--;
							for (i=0; i<m3->mc_snum; i++) {
								m3->mc_pg[i] = m3->mc_pg[i+1];
								m3->mc_ki[i] = m3->mc_ki[i+1];
							}
						}
					}
				}
			} else
				DPUTS("root page doesn't need rebalancing");
			return MDB_SUCCESS;
		}

		// The parent (branch page) must have at least 2 pointers,
		// otherwise the tree is invalid.
		ptop = mc->mc_top-1;
		mdb_cassert(mc, NUMKEYS(mc->mc_pg[ptop]) > 1);

		// Leaf page fill factor is below the threshold.
		// Try to move keys from left or right neighbor, or
		// merge with a neighbor page.

		// Find neighbors.
		mdb_cursor_copy(mc, &mn);
		mn.mc_xcursor = NULL;

		if (mc->mc_ki[ptop] == 0) {
			// We're the leftmost leaf in our parent.
			DPUTS("reading right neighbor");
			mn.mc_ki[ptop]++;
			node = NODEPTR(mc->mc_pg[ptop], mn.mc_ki[ptop]);
			rc = mdb_page_get(mc->mc_txn,NODEPGNO(node),&mn.mc_pg[mn.mc_top],NULL);
			if (rc)
				return rc;
			mn.mc_ki[mn.mc_top] = 0;
			mc->mc_ki[mc->mc_top] = NUMKEYS(mc->mc_pg[mc->mc_top]);
		} else {
			// There is at least one neighbor to the left.
			DPUTS("reading left neighbor");
			mn.mc_ki[ptop]--;
			node = NODEPTR(mc->mc_pg[ptop], mn.mc_ki[ptop]);
			rc = mdb_page_get(mc->mc_txn,NODEPGNO(node),&mn.mc_pg[mn.mc_top],NULL);
			if (rc)
				return rc;
			mn.mc_ki[mn.mc_top] = NUMKEYS(mn.mc_pg[mn.mc_top]) - 1;
			mc->mc_ki[mc->mc_top] = 0;
		}

		DPRINTF(("found neighbor page %"Z"u (%u keys, %.1f%% full)",
		    mn.mc_pg[mn.mc_top]->mp_pgno, NUMKEYS(mn.mc_pg[mn.mc_top]),
			(float)PAGEFILL(mc->mc_txn->mt_env, mn.mc_pg[mn.mc_top]) / 10));

		// If the neighbor page is above threshold and has enough keys,
		// move one key from it. Otherwise we should try to merge them.
		// (A branch page must never have less than 2 keys.)
		minkeys = 1 + (IS_BRANCH(mn.mc_pg[mn.mc_top]));
		if (PAGEFILL(mc->mc_txn->mt_env, mn.mc_pg[mn.mc_top]) >= FILL_THRESHOLD && NUMKEYS(mn.mc_pg[mn.mc_top]) > minkeys)
			return mdb_node_move(&mn, mc);
		else {
			if (mc->mc_ki[ptop] == 0)
				rc = mdb_page_merge(&mn, mc);
			else {
				mn.mc_ki[mn.mc_top] += mc->mc_ki[mn.mc_top] + 1;
				rc = mdb_page_merge(mc, &mn);
				mdb_cursor_copy(&mn, mc);
			}
			mc->mc_flags &= ~(C_INITIALIZED|C_EOF);
		}
		return rc;
	*/
	return nil
}

// Complete a delete operation started by #mdb_cursor_del().
func (c *cursor) del0(leaf *node) error {
	/*
		int rc;
		MDB_page *mp;
		indx_t ki;
		unsigned int nkeys;

		mp = mc->mc_pg[mc->mc_top];
		ki = mc->mc_ki[mc->mc_top];

		// add overflow pages to free list
		if (!IS_LEAF2(mp) && F_ISSET(leaf->mn_flags, F_BIGDATA)) {
			MDB_page *omp;
			pgno_t pg;

			memcpy(&pg, NODEDATA(leaf), sizeof(pg));
			if ((rc = mdb_page_get(mc->mc_txn, pg, &omp, NULL)) ||
				(rc = mdb_ovpage_free(mc, omp)))
				return rc;
		}
		mdb_node_del(mc, mc->mc_db->md_pad);
		mc->mc_db->md_entries--;
		rc = mdb_rebalance(mc);
		if (rc != MDB_SUCCESS)
			mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
		else {
			MDB_cursor *m2, *m3;
			MDB_dbi dbi = mc->mc_dbi;

			mp = mc->mc_pg[mc->mc_top];
			nkeys = NUMKEYS(mp);

			// if mc points past last node in page, find next sibling
			if (mc->mc_ki[mc->mc_top] >= nkeys)
				mdb_cursor_sibling(mc, 1);

			// Adjust other cursors pointing to mp
			for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
				m3 = (mc->mc_flags & C_SUB) ? &m2->mc_xcursor->mx_cursor : m2;
				if (! (m2->mc_flags & m3->mc_flags & C_INITIALIZED))
					continue;
				if (m3 == mc || m3->mc_snum < mc->mc_snum)
					continue;
				if (m3->mc_pg[mc->mc_top] == mp) {
					if (m3->mc_ki[mc->mc_top] >= ki) {
						m3->mc_flags |= C_DEL;
						if (m3->mc_ki[mc->mc_top] > ki)
							m3->mc_ki[mc->mc_top]--;
					}
					if (m3->mc_ki[mc->mc_top] >= nkeys)
						mdb_cursor_sibling(m3, 1);
				}
			}
			mc->mc_flags |= C_DEL;
		}

		return rc;
	*/
	return nil
}

// Split a page and insert a new node.
// @param[in,out] mc Cursor pointing to the page and desired insertion index.
// The cursor will be updated to point to the actual page and index where
// the node got inserted after the split.
// @param[in] newkey The key for the newly inserted node.
// @param[in] newdata The data for the newly inserted node.
// @param[in] newpgno The page number, if the new node is a branch node.
// @param[in] nflags The #NODE_ADD_FLAGS for the new node.
// @return 0 on success, non-zero on failure.
func (c *cursor) splitPage(newKey []byte, newData []byte, newpgno int, nflags int) error {
	/*
		unsigned int flags;
		int		 rc = MDB_SUCCESS, new_root = 0, did_split = 0;
		indx_t		 newindx;
		pgno_t		 pgno = 0;
		int	 i, j, split_indx, nkeys, pmax;
		MDB_env 	*env = mc->mc_txn->mt_env;
		MDB_node	*node;
		MDB_val	 sepkey, rkey, xdata, *rdata = &xdata;
		MDB_page	*copy = NULL;
		MDB_page	*mp, *rp, *pp;
		int ptop;
		MDB_cursor	mn;
		DKBUF;

		mp = mc->mc_pg[mc->mc_top];
		newindx = mc->mc_ki[mc->mc_top];
		nkeys = NUMKEYS(mp);

		DPRINTF(("-----> splitting %s page %"Z"u and adding [%s] at index %i/%i",
		    IS_LEAF(mp) ? "leaf" : "branch", mp->mp_pgno,
		    DKEY(newkey), mc->mc_ki[mc->mc_top], nkeys));

		// Create a right sibling.
		if ((rc = mdb_page_new(mc, mp->mp_flags, 1, &rp)))
			return rc;
		DPRINTF(("new right sibling: page %"Z"u", rp->mp_pgno));

		if (mc->mc_snum < 2) {
			if ((rc = mdb_page_new(mc, P_BRANCH, 1, &pp)))
				return rc;
			// shift current top to make room for new parent
			mc->mc_pg[1] = mc->mc_pg[0];
			mc->mc_ki[1] = mc->mc_ki[0];
			mc->mc_pg[0] = pp;
			mc->mc_ki[0] = 0;
			mc->mc_db->md_root = pp->mp_pgno;
			DPRINTF(("root split! new root = %"Z"u", pp->mp_pgno));
			mc->mc_db->md_depth++;
			new_root = 1;

			// Add left (implicit) pointer.
			if ((rc = mdb_node_add(mc, 0, NULL, NULL, mp->mp_pgno, 0)) != MDB_SUCCESS) {
				// undo the pre-push
				mc->mc_pg[0] = mc->mc_pg[1];
				mc->mc_ki[0] = mc->mc_ki[1];
				mc->mc_db->md_root = mp->mp_pgno;
				mc->mc_db->md_depth--;
				return rc;
			}
			mc->mc_snum = 2;
			mc->mc_top = 1;
			ptop = 0;
		} else {
			ptop = mc->mc_top-1;
			DPRINTF(("parent branch page is %"Z"u", mc->mc_pg[ptop]->mp_pgno));
		}

		mc->mc_flags |= C_SPLITTING;
		mdb_cursor_copy(mc, &mn);
		mn.mc_pg[mn.mc_top] = rp;
		mn.mc_ki[ptop] = mc->mc_ki[ptop]+1;

		if (nflags & MDB_APPEND) {
			mn.mc_ki[mn.mc_top] = 0;
			sepkey = *newkey;
			split_indx = newindx;
			nkeys = 0;
		} else {

			split_indx = (nkeys+1) / 2;

			if (IS_LEAF2(rp)) {
				char *split, *ins;
				int x;
				unsigned int lsize, rsize, ksize;
				// Move half of the keys to the right sibling
				copy = NULL;
				x = mc->mc_ki[mc->mc_top] - split_indx;
				ksize = mc->mc_db->md_pad;
				split = LEAF2KEY(mp, split_indx, ksize);
				rsize = (nkeys - split_indx) * ksize;
				lsize = (nkeys - split_indx) * sizeof(indx_t);
				mp->mp_lower -= lsize;
				rp->mp_lower += lsize;
				mp->mp_upper += rsize - lsize;
				rp->mp_upper -= rsize - lsize;
				sepkey.mv_size = ksize;
				if (newindx == split_indx) {
					sepkey.mv_data = newkey->mv_data;
				} else {
					sepkey.mv_data = split;
				}
				if (x<0) {
					ins = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], ksize);
					memcpy(rp->mp_ptrs, split, rsize);
					sepkey.mv_data = rp->mp_ptrs;
					memmove(ins+ksize, ins, (split_indx - mc->mc_ki[mc->mc_top]) * ksize);
					memcpy(ins, newkey->mv_data, ksize);
					mp->mp_lower += sizeof(indx_t);
					mp->mp_upper -= ksize - sizeof(indx_t);
				} else {
					if (x)
						memcpy(rp->mp_ptrs, split, x * ksize);
					ins = LEAF2KEY(rp, x, ksize);
					memcpy(ins, newkey->mv_data, ksize);
					memcpy(ins+ksize, split + x * ksize, rsize - x * ksize);
					rp->mp_lower += sizeof(indx_t);
					rp->mp_upper -= ksize - sizeof(indx_t);
					mc->mc_ki[mc->mc_top] = x;
					mc->mc_pg[mc->mc_top] = rp;
				}
			} else {
				int psize, nsize, k;
				// Maximum free space in an empty page
				pmax = env->me_psize - PAGEHDRSZ;
				if (IS_LEAF(mp))
					nsize = mdb_leaf_size(env, newkey, newdata);
				else
					nsize = mdb_branch_size(env, newkey);
				nsize = EVEN(nsize);

				// grab a page to hold a temporary copy
				copy = mdb_page_malloc(mc->mc_txn, 1);
				if (copy == NULL)
					return ENOMEM;
				copy->mp_pgno  = mp->mp_pgno;
				copy->mp_flags = mp->mp_flags;
				copy->mp_lower = PAGEHDRSZ;
				copy->mp_upper = env->me_psize;

				// prepare to insert
				for (i=0, j=0; i<nkeys; i++) {
					if (i == newindx) {
						copy->mp_ptrs[j++] = 0;
					}
					copy->mp_ptrs[j++] = mp->mp_ptrs[i];
				}

				// When items are relatively large the split point needs
				// to be checked, because being off-by-one will make the
				// difference between success or failure in mdb_node_add.
				//
				// It's also relevant if a page happens to be laid out
				// such that one half of its nodes are all "small" and
				// the other half of its nodes are "large." If the new
				// item is also "large" and falls on the half with
				// "large" nodes, it also may not fit.
				//
				// As a final tweak, if the new item goes on the last
				// spot on the page (and thus, onto the new page), bias
				// the split so the new page is emptier than the old page.
				// This yields better packing during sequential inserts.
				if (nkeys < 20 || nsize > pmax/16 || newindx >= nkeys) {
					// Find split point
					psize = 0;
					if (newindx <= split_indx || newindx >= nkeys) {
						i = 0; j = 1;
						k = newindx >= nkeys ? nkeys : split_indx+2;
					} else {
						i = nkeys; j = -1;
						k = split_indx-1;
					}
					for (; i!=k; i+=j) {
						if (i == newindx) {
							psize += nsize;
							node = NULL;
						} else {
							node = (MDB_node *)((char *)mp + copy->mp_ptrs[i]);
							psize += NODESIZE + NODEKSZ(node) + sizeof(indx_t);
							if (IS_LEAF(mp)) {
								if (F_ISSET(node->mn_flags, F_BIGDATA))
									psize += sizeof(pgno_t);
								else
									psize += NODEDSZ(node);
							}
							psize = EVEN(psize);
						}
						if (psize > pmax || i == k-j) {
							split_indx = i + (j<0);
							break;
						}
					}
				}
				if (split_indx == newindx) {
					sepkey.mv_size = newkey->mv_size;
					sepkey.mv_data = newkey->mv_data;
				} else {
					node = (MDB_node *)((char *)mp + copy->mp_ptrs[split_indx]);
					sepkey.mv_size = node->mn_ksize;
					sepkey.mv_data = NODEKEY(node);
				}
			}
		}

		DPRINTF(("separator is %d [%s]", split_indx, DKEY(&sepkey)));

		// Copy separator key to the parent.
		if (SIZELEFT(mn.mc_pg[ptop]) < mdb_branch_size(env, &sepkey)) {
			mn.mc_snum--;
			mn.mc_top--;
			did_split = 1;
			rc = mdb_page_split(&mn, &sepkey, NULL, rp->mp_pgno, 0);

			// root split?
			if (mn.mc_snum == mc->mc_snum) {
				mc->mc_pg[mc->mc_snum] = mc->mc_pg[mc->mc_top];
				mc->mc_ki[mc->mc_snum] = mc->mc_ki[mc->mc_top];
				mc->mc_pg[mc->mc_top] = mc->mc_pg[ptop];
				mc->mc_ki[mc->mc_top] = mc->mc_ki[ptop];
				mc->mc_snum++;
				mc->mc_top++;
				ptop++;
			}
			// Right page might now have changed parent.
			// Check if left page also changed parent.
			if (mn.mc_pg[ptop] != mc->mc_pg[ptop] &&
			    mc->mc_ki[ptop] >= NUMKEYS(mc->mc_pg[ptop])) {
				for (i=0; i<ptop; i++) {
					mc->mc_pg[i] = mn.mc_pg[i];
					mc->mc_ki[i] = mn.mc_ki[i];
				}
				mc->mc_pg[ptop] = mn.mc_pg[ptop];
				mc->mc_ki[ptop] = mn.mc_ki[ptop] - 1;
			}
		} else {
			mn.mc_top--;
			rc = mdb_node_add(&mn, mn.mc_ki[ptop], &sepkey, NULL, rp->mp_pgno, 0);
			mn.mc_top++;
		}
		mc->mc_flags ^= C_SPLITTING;
		if (rc != MDB_SUCCESS) {
			return rc;
		}
		if (nflags & MDB_APPEND) {
			mc->mc_pg[mc->mc_top] = rp;
			mc->mc_ki[mc->mc_top] = 0;
			rc = mdb_node_add(mc, 0, newkey, newdata, newpgno, nflags);
			if (rc)
				return rc;
			for (i=0; i<mc->mc_top; i++)
				mc->mc_ki[i] = mn.mc_ki[i];
		} else if (!IS_LEAF2(mp)) {
			// Move nodes
			mc->mc_pg[mc->mc_top] = rp;
			i = split_indx;
			j = 0;
			do {
				if (i == newindx) {
					rkey.mv_data = newkey->mv_data;
					rkey.mv_size = newkey->mv_size;
					if (IS_LEAF(mp)) {
						rdata = newdata;
					} else
						pgno = newpgno;
					flags = nflags;
					// Update index for the new key.
					mc->mc_ki[mc->mc_top] = j;
				} else {
					node = (MDB_node *)((char *)mp + copy->mp_ptrs[i]);
					rkey.mv_data = NODEKEY(node);
					rkey.mv_size = node->mn_ksize;
					if (IS_LEAF(mp)) {
						xdata.mv_data = NODEDATA(node);
						xdata.mv_size = NODEDSZ(node);
						rdata = &xdata;
					} else
						pgno = NODEPGNO(node);
					flags = node->mn_flags;
				}

				if (!IS_LEAF(mp) && j == 0) {
					// First branch index doesn't need key data.
					rkey.mv_size = 0;
				}

				rc = mdb_node_add(mc, j, &rkey, rdata, pgno, flags);
				if (rc) {
					// return tmp page to freelist
					mdb_page_free(env, copy);
					return rc;
				}
				if (i == nkeys) {
					i = 0;
					j = 0;
					mc->mc_pg[mc->mc_top] = copy;
				} else {
					i++;
					j++;
				}
			} while (i != split_indx);

			nkeys = NUMKEYS(copy);
			for (i=0; i<nkeys; i++)
				mp->mp_ptrs[i] = copy->mp_ptrs[i];
			mp->mp_lower = copy->mp_lower;
			mp->mp_upper = copy->mp_upper;
			memcpy(NODEPTR(mp, nkeys-1), NODEPTR(copy, nkeys-1),
				env->me_psize - copy->mp_upper);

			// reset back to original page
			if (newindx < split_indx) {
				mc->mc_pg[mc->mc_top] = mp;
				if (nflags & MDB_RESERVE) {
					node = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
					if (!(node->mn_flags & F_BIGDATA))
						newdata->mv_data = NODEDATA(node);
				}
			} else {
				mc->mc_pg[mc->mc_top] = rp;
				mc->mc_ki[ptop]++;
				// Make sure mc_ki is still valid.
				if (mn.mc_pg[ptop] != mc->mc_pg[ptop] &&
					mc->mc_ki[ptop] >= NUMKEYS(mc->mc_pg[ptop])) {
					for (i=0; i<ptop; i++) {
						mc->mc_pg[i] = mn.mc_pg[i];
						mc->mc_ki[i] = mn.mc_ki[i];
					}
					mc->mc_pg[ptop] = mn.mc_pg[ptop];
					mc->mc_ki[ptop] = mn.mc_ki[ptop] - 1;
				}
			}
			// return tmp page to freelist
			mdb_page_free(env, copy);
		}

		{
			// Adjust other cursors pointing to mp
			MDB_cursor *m2, *m3;
			MDB_dbi dbi = mc->mc_dbi;
			int fixup = NUMKEYS(mp);

			for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
				if (mc->mc_flags & C_SUB)
					m3 = &m2->mc_xcursor->mx_cursor;
				else
					m3 = m2;
				if (m3 == mc)
					continue;
				if (!(m2->mc_flags & m3->mc_flags & C_INITIALIZED))
					continue;
				if (m3->mc_flags & C_SPLITTING)
					continue;
				if (new_root) {
					int k;
					// root split
					for (k=m3->mc_top; k>=0; k--) {
						m3->mc_ki[k+1] = m3->mc_ki[k];
						m3->mc_pg[k+1] = m3->mc_pg[k];
					}
					if (m3->mc_ki[0] >= split_indx) {
						m3->mc_ki[0] = 1;
					} else {
						m3->mc_ki[0] = 0;
					}
					m3->mc_pg[0] = mc->mc_pg[0];
					m3->mc_snum++;
					m3->mc_top++;
				}
				if (m3->mc_top >= mc->mc_top && m3->mc_pg[mc->mc_top] == mp) {
					if (m3->mc_ki[mc->mc_top] >= newindx && !(nflags & MDB_SPLIT_REPLACE))
						m3->mc_ki[mc->mc_top]++;
					if (m3->mc_ki[mc->mc_top] >= fixup) {
						m3->mc_pg[mc->mc_top] = rp;
						m3->mc_ki[mc->mc_top] -= fixup;
						m3->mc_ki[ptop] = mn.mc_ki[ptop];
					}
				} else if (!did_split && m3->mc_top >= ptop && m3->mc_pg[ptop] == mc->mc_pg[ptop] &&
					m3->mc_ki[ptop] >= mc->mc_ki[ptop]) {
					m3->mc_ki[ptop]++;
				}
			}
		}
		DPRINTF(("mp left: %d, rp left: %d", SIZELEFT(mp), SIZELEFT(rp)));
		return rc;
	*/
	return nil
}

// Add all the DB's pages to the free list.
// @param[in] mc Cursor on the DB to free.
// @param[in] subs non-Zero to check for sub-DBs in this DB.
// @return 0 on success, non-zero on failure.
func (c *cursor) drop0(subs int) error {
	/*
		int rc;

		rc = mdb_page_search(mc, NULL, MDB_PS_FIRST);
		if (rc == MDB_SUCCESS) {
			MDB_txn *txn = mc->mc_txn;
			MDB_node *ni;
			MDB_cursor mx;
			unsigned int i;

			// LEAF2 pages have no nodes, cannot have sub-DBs
			if (IS_LEAF2(mc->mc_pg[mc->mc_top]))
				mdb_cursor_pop(mc);

			mdb_cursor_copy(mc, &mx);
			while (mc->mc_snum > 0) {
				MDB_page *mp = mc->mc_pg[mc->mc_top];
				unsigned n = NUMKEYS(mp);
				if (IS_LEAF(mp)) {
					for (i=0; i<n; i++) {
						ni = NODEPTR(mp, i);
						if (ni->mn_flags & F_BIGDATA) {
							MDB_page *omp;
							pgno_t pg;
							memcpy(&pg, NODEDATA(ni), sizeof(pg));
							rc = mdb_page_get(txn, pg, &omp, NULL);
							if (rc != 0)
								return rc;
							mdb_cassert(mc, IS_OVERFLOW(omp));
							rc = mdb_midl_append_range(&txn->mt_free_pgs,
								pg, omp->mp_pages);
							if (rc)
								return rc;
						} else if (subs && (ni->mn_flags & F_SUBDATA)) {
							mdb_xcursor_init1(mc, ni);
							rc = mdb_drop0(&mc->mc_xcursor->mx_cursor, 0);
							if (rc)
								return rc;
						}
					}
				} else {
					if ((rc = mdb_midl_need(&txn->mt_free_pgs, n)) != 0)
						return rc;
					for (i=0; i<n; i++) {
						pgno_t pg;
						ni = NODEPTR(mp, i);
						pg = NODEPGNO(ni);
						// free it
						mdb_midl_xappend(txn->mt_free_pgs, pg);
					}
				}
				if (!mc->mc_top)
					break;
				mc->mc_ki[mc->mc_top] = i;
				rc = mdb_cursor_sibling(mc, 1);
				if (rc) {
					// no more siblings, go back to beginning
					// of previous level.
					mdb_cursor_pop(mc);
					mc->mc_ki[0] = 0;
					for (i=1; i<mc->mc_snum; i++) {
						mc->mc_ki[i] = 0;
						mc->mc_pg[i] = mx.mc_pg[i];
					}
				}
			}
			// free it
			rc = mdb_midl_append(&txn->mt_free_pgs, mc->mc_db->md_root);
		} else if (rc == MDB_NOTFOUND) {
			rc = MDB_SUCCESS;
		}
		return rc;
	*/
	return nil
}