Add inline documentation for bdc109b.

This commit simply adds some additional comments to the commit provided
by sasha-s that fixes the "slice out of bounds" errors.

bolt_amd64.go

@@ -5,7 +5,3 @@ const maxMapSize = 0xFFFFFFFFFFFF // 256TB
 
 // maxAllocSize is the size used when creating array pointers.
 const maxAllocSize = 0x7FFFFFFF
-
-// Setting
-// const maxAllocSize = 70000
-// reveals the index out of bound bug(s)

node.go

@@ -220,16 +220,21 @@ func (n *node) write(p *page) {
 			elem.pgid = item.pgid
 			_assert(elem.pgid != p.id, "write: circular dependency occurred")
 		}
-		lk, lv := len(item.key), len(item.value)
-		if len(b) < lk+lv {
+
+		// If the length of key+value is larger than the max allocation size
+		// then we need to reallocate the byte array pointer.
+		//
+		// See: https://github.com/boltdb/bolt/pull/335
+		klen, vlen := len(item.key), len(item.value)
+		if len(b) < klen+vlen {
 			b = (*[maxAllocSize]byte)(unsafe.Pointer(&b[0]))[:]
 		}
 
 		// Write data for the element to the end of the page.
 		copy(b[0:], item.key)
-		b = b[lk:]
+		b = b[klen:]
 		copy(b[0:], item.value)
-		b = b[lv:]
+		b = b[vlen:]
 	}
 
 	// DEBUG ONLY: n.dump()
@@ -355,9 +360,7 @@ func (n *node) spill() error {
 		}
 
 		// Allocate contiguous space for the node.
-		// sz := node.size() + n.pageElementSize()*len(n.inodes)
-		sz := node.size()
-		p, err := tx.allocate((sz / tx.db.pageSize) + 1)
+		p, err := tx.allocate((node.size() / tx.db.pageSize) + 1)
 		if err != nil {
 			return err
 		}

tx.go

@@ -422,26 +422,38 @@ func (tx *Tx) write() error {
 	for _, p := range pages {
 		size := (int(p.overflow) + 1) * tx.db.pageSize
 		offset := int64(p.id) * int64(tx.db.pageSize)
+
+		// Write out page in "max allocation" sized chunks.
 		ptr := (*[maxAllocSize]byte)(unsafe.Pointer(p))
 		for {
+			// Limit our write to our max allocation size.
 			sz := size
 			if sz > maxAllocSize-1 {
 				sz = maxAllocSize - 1
 			}
+
+			// Write chunk to disk.
 			buf := ptr[:sz]
 			if _, err := tx.db.ops.writeAt(buf, offset); err != nil {
 				return err
 			}
+
 			// Update statistics.
 			tx.stats.Write++
+
+			// Exit inner for loop if we've written all the chunks.
 			size -= sz
 			if size == 0 {
 				break
 			}
+
+			// Otherwise move offset forward and move pointer to next chunk.
 			offset += int64(sz)
 			ptr = (*[maxAllocSize]byte)(unsafe.Pointer(&ptr[sz]))
 		}
 	}
+
+	// Ignore file sync if flag is set on DB.
 	if !tx.db.NoSync || IgnoreNoSync {
 		if err := fdatasync(tx.db); err != nil {
 			return err