Bolt is a pure Go key/value store inspired by Howard Chu's LMDB project. The goal of the project is to provide a simple, fast, and reliable database for projects that don't require a full database server such as Postgres or MySQL.
Since Bolt is meant to be used as such a low-level piece of functionality, simplicity is key. The API will be small and only focus on getting values and setting values. That's it.
Bolt is stable, the API is fixed, and the file format is fixed. Full unit test coverage and randomized black box testing are used to ensure database consistency and thread safety. Bolt is currently used in high-load production environments serving databases as large as 1TB. Many companies such as Shopify and Heroku use Bolt-backed services every day.
- Getting Started
- Resources
- Comparison with other databases
- Caveats & Limitations
- Reading the Source
- Other Projects Using Bolt
To start using Bolt, install Go and run go get
:
$ go get github.com/boltdb/bolt/...
This will retrieve the library and install the bolt
command line utility into
your $GOBIN
path.
The top-level object in Bolt is a DB
. It is represented as a single file on
your disk and represents a consistent snapshot of your data.
To open your database, simply use the bolt.Open()
function:
package main
import (
"log"
"github.com/boltdb/bolt"
)
func main() {
// Open the my.db data file in your current directory.
// It will be created if it doesn't exist.
db, err := bolt.Open("my.db", 0600, nil)
if err != nil {
log.Fatal(err)
}
defer db.Close()
...
}
Please note that Bolt obtains a file lock on the data file so multiple processes
cannot open the same database at the same time. Opening an already open Bolt
database will cause it to hang until the other process closes it. To prevent
an indefinite wait you can pass a timeout option to the Open()
function:
db, err := bolt.Open("my.db", 0600, &bolt.Options{Timeout: 1 * time.Second})
Bolt allows only one read-write transaction at a time but allows as many read-only transactions as you want at a time. Each transaction has a consistent view of the data as it existed when the transaction started.
Individual transactions and all objects created from them (e.g. buckets, keys)
are not thread safe. To work with data in multiple goroutines you must start
a transaction for each one or use locking to ensure only one goroutine accesses
a transaction at a time. Creating transaction from the DB
is thread safe.
Read-only transactions and read-write transactions should not depend on one another and generally shouldn't be opened simultaneously in the same goroutine. This can cause a deadlock as the read-write transaction needs to periodically re-map the data file but it cannot do so while a read-only transaction is open.
To start a read-write transaction, you can use the DB.Update()
function:
err := db.Update(func(tx *bolt.Tx) error {
...
return nil
})
Inside the closure, you have a consistent view of the database. You commit the
transaction by returning nil
at the end. You can also rollback the transaction
at any point by returning an error. All database operations are allowed inside
a read-write transaction.
Always check the return error as it will report any disk failures that can cause your transaction to not complete. If you return an error within your closure it will be passed through.
To start a read-only transaction, you can use the DB.View()
function:
err := db.View(func(tx *bolt.Tx) error {
...
return nil
})
You also get a consistent view of the database within this closure, however, no mutating operations are allowed within a read-only transaction. You can only retrieve buckets, retrieve values, and copy the database within a read-only transaction.
Each DB.Update()
waits for disk to commit the writes. This overhead
can be minimized by combining multiple updates with the DB.Batch()
function:
err := db.Batch(func(tx *bolt.Tx) error {
...
return nil
})