Add freelist cache.

This commit adds a cache to the freelist which combines the available free pages and pending free pages in
a single map. This was added to improve performance where freelist.isFree() was consuming 70% of CPU time
for large freelists.

1 files changed, 1 insertions, 1 deletions

diff --git a/db.go b/db.go
index 6ef35ea..4d7ec12 100644
--- a/db.go
+++ b/db.go
@@ -144,7 +144,7 @@ func Open(path string, mode os.FileMode, options *Options) (*DB, error) {
 	}
 
 	// Read in the freelist.
-	db.freelist = &freelist{pending: make(map[txid][]pgid)}
+	db.freelist = newFreelist()
 	db.freelist.read(db.page(db.meta().freelist))
 
 	// Mark the database as opened and return.