do not grow dbsize agressively

Only grow the database size when the high watermark increases.
We also grows the database size a little bit aggressively to
save a few ftruncates.

I have tested this on various environments. The performance impact
is ignorable with 16MB over allocation. Without over allocation,
the performance might decrease 100% when each Tx.Commit needs a new
page on a very slow disk (seek time dominates the total write).

1 files changed, 6 insertions, 0 deletions

diff --git a/tx.go b/tx.go
index cb60149..80d9799 100644
--- a/tx.go
+++ b/tx.go
@@ -157,6 +157,8 @@ func (tx *Tx) Commit() error {
 	// Free the old root bucket.
 	tx.meta.root.root = tx.root.root
 
+	opgid := tx.meta.pgid
+
 	// Free the freelist and allocate new pages for it. This will overestimate
 	// the size of the freelist but not underestimate the size (which would be bad).
 	tx.db.freelist.free(tx.meta.txid, tx.db.page(tx.meta.freelist))
@@ -171,6 +173,10 @@ func (tx *Tx) Commit() error {
 	}
 	tx.meta.freelist = p.id
 
+	if tx.meta.pgid > opgid {
+		tx.db.growSize(int(tx.meta.pgid+1) * tx.db.pageSize)
+	}
+
 	// Write dirty pages to disk.
 	startTime = time.Now()
 	if err := tx.write(); err != nil {