BoltDB

View Current Viewing Revision #17 from 11/24/2019 9:39 p.m.

BoltDB is an embedded key/value database written in Go. It supports fully serializable transactions, ACID semantics, and lock-free MVCC with multiple readers and a single writer. BoltDB uses a single-level, zero-copy, B+tree data storage, which allows fast read access and does not require recovery in the event of a system crash.

History

In 2011, Howard Chu introduced MDB, a memory-mapped database backend for OpenLDAP, later renamed to [LMDB] (https://symas.com/lmdb/technical/)(Lightning Memory-Mapped Database). In 2013, BoltDB was initially started by Ben Johnson as a port of LMDB to Go, but then the two projects diverged as the author of Bolt decided to focus on simplicity and providing the easy-to-use Go API. The goal of BoltDB became to provide a simple, fast, and reliable database for projects that don't require a full database server such as Postgres or MySQL. With BoltDB being stable, its API fixed, and its file format fixed, the author considered the project a success. Leaving it in such a state, the project was abandoned by its author in 2017.

BoltDB saves data into a single memory-mapped file on disk. Write-ahead log is not necessary since BoltDB only deals with one file at a time. With copy-on-write, when writing to a page, BoltDB makes updates on the copy of the original page and updates the pointer to point at the new page upon commit.

Isolation Levels

Serializable

BoltDB supports fully serializable ACID transactions. It allows only one read-write transaction at a time but allows as many read-only transactions as requested.

When opening a database with bolt.Open(), BoltDB 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. BoltDB supports the ability to prevent an indefinite wait by passing a timeout option to the Open() function.

Checkpoints

Not Supported

Storage Model

Custom

BoltDB uses key/value storage, which does not involve rows or columns.

Concurrency Control

Multi-version Concurrency Control (MVCC)

BoltDB allows only one read-write transaction at a time.

Data Model

Key/Value

Bolt is a key-value store that provides an ordered map, which allows easy access and lookup.

Query Interface

Custom API

Views

Virtual Views

Bolt allows only one read-write transaction at a time but allows as many read-only transactions as requested. Each transaction has a consistent view of the data as it existed when the transaction started. BoltDB recommends three types of transactions: read-write transactions with DB.Update, read-only transactions with DB.View and batch read-write transactions with DB.Batch. Along with the three recommended transactions, BoltDB also allows manual transaction management with DB.Begin.