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, 0 insertions, 11 deletions

diff --git a/bolt_unix.go b/bolt_unix.go
index 6eef6b2..5a199c7 100644
--- a/bolt_unix.go
+++ b/bolt_unix.go
@@ -46,17 +46,6 @@ func funlock(f *os.File) error {
 
 // mmap memory maps a DB's data file.
 func mmap(db *DB, sz int) error {
-	// Truncate and fsync to ensure file size metadata is flushed.
-	// https://github.com/boltdb/bolt/issues/284
-	if !db.NoGrowSync && !db.readOnly {
-		if err := db.file.Truncate(int64(sz)); err != nil {
-			return fmt.Errorf("file resize error: %s", err)
-		}
-		if err := db.file.Sync(); err != nil {
-			return fmt.Errorf("file sync error: %s", err)
-		}
-	}
-
 	// Map the data file to memory.
 	b, err := syscall.Mmap(int(db.file.Fd()), 0, sz, syscall.PROT_READ, syscall.MAP_SHARED)
 	if err != nil {