bbolt

Shape: copy-on-write B+tree, single file, pure Go Repository: github.com/etcd-io/bbolt

bbolt is a single-file B+tree, the storage layer under etcd and a long list of Go projects that want a dependable embedded store with no moving parts. It is the simplest engine in this set: one file, one B+tree, a copy-on-write design that gives you a consistent snapshot for free.

Its strength is reading in order. Because neighbouring keys sit in neighbouring pages, an ordered scan is close to a sequential disk read, and bbolt scans faster than anything else here.

Best at

• Ordered scans. 766,000 keys/sec, the fastest scanner measured. See range scans.
• Read-mostly simplicity. 865,000 random reads/sec from a single file with zero configuration.
• Consistent snapshots. The copy-on-write design means a read transaction sees a stable view while writes continue.

Watch out for

• Slow random writes. 38,000 writes/sec, near the bottom, because a copy-on-write B+tree copies a path of pages on each commit.
• Slowest durable writes. 110 per second with a flush on every commit, the floor in this set.
• Space. 2.3x the data, the page-level overhead of a B+tree.

Reach for it when

You want a rock-solid single-file store for a read-mostly or scan-heavy workload and your write rate is modest. It is the boring, dependable choice, and boring is often correct. If you need heavy writes alongside the scans, look at pebble instead.