Fix bucket reclamation.

The bucket page is allocated separately from the rest of the pages but the old bucket pages were
not being added to the freelist. This change fixes that and adds a simple check for database
consistency. More advanced consistency checks can be added in the future.

Fixes #82.

db_test.go

@@ -244,11 +244,11 @@ func TestDBStat(t *testing.T) {
 		// Obtain stats.
 		stat, err := db.Stat()
 		assert.NoError(t, err)
-		assert.Equal(t, stat.PageCount, 128)
-		assert.Equal(t, stat.FreePageCount, 2)
-		assert.Equal(t, stat.PageSize, 4096)
-		assert.Equal(t, stat.MmapSize, 4194304)
-		assert.Equal(t, stat.TxCount, 2)
+		assert.Equal(t, 126, stat.PageCount)
+		assert.Equal(t, 3, stat.FreePageCount)
+		assert.Equal(t, 4096, stat.PageSize)
+		assert.Equal(t, 4194304, stat.MmapSize)
+		assert.Equal(t, 2, stat.TxCount)
 
 		// Close readers.
 		t0.Rollback()
@@ -282,6 +282,48 @@ func TestDBMmapSize(t *testing.T) {
 	assert.Equal(t, db.mmapSize(1<<30), 1<<31)
 }
 
+// Ensure that database pages are in expected order and type.
+func TestDBConsistency(t *testing.T) {
+	withOpenDB(func(db *DB, path string) {
+		db.Update(func(tx *Tx) error {
+			return tx.CreateBucket("widgets")
+		})
+
+		for i := 0; i < 10; i++ {
+			db.Update(func(tx *Tx) error {
+				assert.NoError(t, tx.Bucket("widgets").Put([]byte("foo"), []byte("bar")))
+				return nil
+			})
+		}
+		db.Update(func(tx *Tx) error {
+			if p, _ := tx.Page(0); assert.NotNil(t, p) {
+				assert.Equal(t, "meta", p.Type)
+			}
+			if p, _ := tx.Page(1); assert.NotNil(t, p) {
+				assert.Equal(t, "meta", p.Type)
+			}
+			if p, _ := tx.Page(2); assert.NotNil(t, p) {
+				assert.Equal(t, "freelist", p.Type)
+			}
+			if p, _ := tx.Page(3); assert.NotNil(t, p) {
+				assert.Equal(t, "free", p.Type)
+			}
+			if p, _ := tx.Page(4); assert.NotNil(t, p) {
+				assert.Equal(t, "buckets", p.Type)
+			}
+			if p, _ := tx.Page(5); assert.NotNil(t, p) {
+				assert.Equal(t, "leaf", p.Type)
+			}
+			if p, _ := tx.Page(6); assert.NotNil(t, p) {
+				assert.Equal(t, "free", p.Type)
+			}
+			p, _ := tx.Page(7)
+			assert.Nil(t, p)
+			return nil
+		})
+	})
+}
+
 // Ensure that a database can return a string representation of itself.
 func TestDBString(t *testing.T) {
 	db := &DB{path: "/tmp/foo"}

tx.go

@@ -195,14 +195,15 @@ func (t *Tx) Commit() error {
 	}
 	t.buckets.write(p)
 
+	// Free previous bucket page and update meta.
+	t.db.freelist.free(t.id(), t.page(t.meta.buckets))
+	t.meta.buckets = p.id
+
 	// Write dirty pages to disk.
 	if err := t.write(); err != nil {
 		return err
 	}
 
-	// Update the meta.
-	t.meta.buckets = p.id
-
 	// Write meta to disk.
 	if err := t.writeMeta(); err != nil {
 		return err

tx_test.go

@@ -230,7 +230,7 @@ func TestTxDeleteBucket(t *testing.T) {
 
 		db.Update(func(tx *Tx) error {
 			// Verify that the bucket's page is free.
-			assert.Equal(t, []pgid{root}, db.freelist.all())
+			assert.Equal(t, []pgid{6, root, 3}, db.freelist.all())
 
 			// Create the bucket again and make sure there's not a phantom value.
 			assert.NoError(t, tx.CreateBucket("widgets"))