BoltDB

View Current Viewing Revision #18 from 11/24/2019 10 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.

Indexes

B+Tree

Logging

Not Supported

Bolt saves data into a single memory-mapped file on disk. It doesn’t have a separate journal or write-ahead log.

Data Model

Key/Value

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

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.

Joins

Not Supported

Storage Model

Custom

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

Checkpoints

Not Supported

Concurrency Control

Multi-version Concurrency Control (MVCC)

BoltDB supports lock-free MVCC using a single writer and multiple readers. It allows only one read-write transaction at a time but allows multiple read-only transactions at the same time. 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.

Query Compilation

Not Supported

Storage Organization

Copy-on-Write / Shadow Paging

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.

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.