Bolt [![Coverage Status](https://coveralls.io/repos/boltdb/bolt/badge.svg?branch=master)](https://coveralls.io/r/boltdb/bolt?branch=master) [![GoDoc](https://godoc.org/github.com/boltdb/bolt?status.svg)](https://godoc.org/github.com/boltdb/bolt) ![Version](https://img.shields.io/badge/version-1.0-green.svg)
====
Bolt is a pure Go key/value store inspired by [Howard Chu's][hyc_symas]
[LMDB project][lmdb]. 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.
[hyc_symas]: https://twitter.com/hyc_symas
[lmdb]: http://symas.com/mdb/
## Project Status
Bolt is stable and the API is fixed. Full unit test coverage and randomized
black box testing are used to ensure database consistency and thread safety.
Bolt is currently in high-load production environments serving databases as
large as 1TB. Many companies such as Shopify and Heroku use Bolt-backed
services every day.
## Table of Contents
- [Getting Started](#getting-started)
- [Installing](#installing)
- [Opening a database](#opening-a-database)
- [Transactions](#transactions)
- [Read-write transactions](#read-write-transactions)
- [Read-only transactions](#read-only-transactions)
- [Batch read-write transactions](#batch-read-write-transactions)
- [Managing transactions manually](#managing-transactions-manually)
- [Using buckets](#using-buckets)
- [Using key/value pairs](#using-keyvalue-pairs)
- [Autoincrementing integer for the bucket](#autoincrementing-integer-for-the-bucket)
- [Iterating over keys](#iterating-over-keys)
- [Prefix scans](#prefix-scans)
- [Range scans](#range-scans)
- [ForEach()](#foreach)
- [Nested buckets](#nested-buckets)
- [Database backups](#database-backups)
- [Statistics](#statistics)
- [Read-Only Mode](#read-only-mode)
- [Mobile Use (iOS/Android)](#mobile-use-iosandroid)
- [Resources](#resources)
- [Comparison with other databases](#comparison-with-other-databases)
- [Postgres, MySQL, & other relational databases](#postgres-mysql--other-relational-databases)
- [LevelDB, RocksDB](#leveldb-rocksdb)
- [LMDB](#lmdb)
- [Caveats & Limitations](#caveats--limitations)
- [Reading the Source](#reading-the-source)
- [Other Projects Using Bolt](#other-projects-using-bolt)
## Getting Started
### Installing
To start using Bolt, install Go and run `go get`:
```sh
$ go get github.com/boltdb/bolt/...
```
This will retrieve the library and install the `bolt` command line utility into
your `$GOBIN` path.
### Opening a database
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:
```go
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:
```go
db, err := bolt.Open("my.db", 0600, &bolt.Options{Timeout: 1 * time.Second})
```
### Transactions
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.
#### Read-write transactions
To start a read-write transaction, you can use the `DB.Update()` function:
```go
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.
#### Read-only transactions
To start a read-only transaction, you can use the `DB.View()` function:
```go
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.
#### Batch read-write transactions
Each `DB.Update()` waits for disk to commit the writes. This overhead
can be minimized by combining multiple updates with the `DB.Batch()`
function:
```go
err := db.Batch(func(tx *bolt.Tx) error {
...
return nil
})
```
Concurrent Batch calls are opportunistically combined into larger
transactions. Batch is only useful when there are multiple goroutines
calling it.
The trade-off is that `Batch` can call the given
function multiple times, if parts of the transaction fail. The
function must be idempotent and side effects must take effect only
after a successful return from `DB.Batch()`.
For example: don't display messages from inside the function, instead
set variables in the enclosing scope:
```go
var id uint64
err := db.Batch(func(tx *bolt.Tx) error {
// Find last key in bucket, decode as bigendian uint64, increment
// by one, encode back to []byte, and add new key.
...
id = newValue
return nil
})
if err != nil {
return ...
}
fmt.Println("Allocated ID %d", id)
```
#### Managing transactions manually
The `DB.View()` and `DB.Update()` functions are wrappers around the `DB.Begin()`
function. These helper functions will start the transaction, execute a function,
and then safely close your transaction if an error is returned. This is the
recommended way to use Bolt transactions.
However, sometimes you may want to manually start and end your transactions.
You can use the `Tx.Begin()` function directly but **please** be sure to close
the transaction.
```go
// Start a writable transaction.
tx, err := db.Begin(true)
if err != nil {
return err
}
defer tx.Rollback()
// Use the transaction...
_, err := tx.CreateBucket([]byte("MyBucket"))
if err != nil {
return err
}
// Commit the transaction and check for error.
if err := tx.Commit(); err != nil {
return err
}
```
The first argument to `DB.Begin()` is a boolean stating if the transaction
should be writable.
### Using buckets
Buckets are collections of key/value pairs within the database. All keys in a
bucket must be unique. You can create a bucket using the `DB.CreateBucket()`
function:
```go
db.Update(func(tx *bolt.Tx) error {
b, err := tx.CreateBucket([]byte("MyBucket"))
if err != nil {
return fmt.Errorf("create bucket: %s", err)
}
return nil
})
```
You can also create a bucket only if it doesn't exist by using the
`Tx.CreateBucketIfNotExists()` functio
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message
message.proto 479B
ext_message.go 1KB
message.pb.go 11KB
tools
utils.go 453B
define.go 3KB
test.go 165B
stop.sh 32B
store
store_service.go 747B
file_mmap_store.go 2KB
file_store.go 4KB
file_store_writer.go 2KB
file_mmap_reader.go 2KB
index
segment
segment_service.go 457B
segment.go 4KB
segment_test.go 1KB
index_test.go 817B
invert
invert_test.go 4KB
memory_doc_list.go 2KB
invert_writer.go 2KB
invert_reader.go 1KB
invert_service.go 1KB
invert_set.go 7KB
index_service.go 438B
index.go 5KB
dict
dict_map_test.go 1KB
dict_service.go 860B
dict_map.go 4KB
src
FalconIndexLib
segment
invert.go 12KB
segment.go 19KB
field.go 9KB
profile.go 17KB
shard.go 973B
index.go 17KB
FalconService
httpService.go 8KB
tree
btree.go 3KB
bolt
freelist.go 6KB
bolt_arm64.go 236B
bolt_ppc64le.go 238B
bolt_unix.go 2KB
bolt_386.go 212B
boltsync_unix.go 169B
bolt_s390x.go 236B
bolt_unix_solaris.go 2KB
bolt_windows.go 4KB
bucket.go 20KB
bolt_openbsd.go 518B
Makefile 410B
LICENSE 1KB
db.go 28KB
bolt_linux.go 171B
bolt_amd64.go 219B
node.go 16KB
page.go 4KB
cmd
bolt
main_test.go 5KB
main.go 38KB
bolt_ppc64.go 236B
cursor.go 11KB
errors.go 3KB
doc.go 2KB
bolt_ppc.go 227B
bolt_arm.go 212B
tx.go 18KB
appveyor.yml 262B
README.md 32KB
FalconSearch
falcon.go 2KB
utils
JsonFileIO.go 2KB
convert.go 2KB
Utils.go 16KB
BitMap.go 4KB
Mmap.go 7KB
log4FE.go 2KB
Segmenter.go 4KB
BoltHelper.go 8KB
tools.go 2KB
FalconDispatcher
Dispatcher.go 13KB
FalconEngine
defaultEngine.go 15KB
start.sh 40B
install.sh 38B
binlog
binlog_service.go 725B
mlog
mlog.go 7KB
util
basic_data_test.go 201B
basic_interface.go 2KB
basic_data.go 385B
README.md 8KB
main.go 179B
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