cdb: Intro (original) (raw)

cdb: Intro

cdb is a fast, reliable, simple package for creating and reading constant databases. The cdb database structure provides several features:

• Fast lookups: A successful lookup in a large database normally takes just two disk accesses. An unsuccessful lookup takes only one.
• Low overhead: A database uses 2048 bytes (or 4096 bytes for cdb64), plus 24 bytes per record (or 48 bytes per record for cdb64), plus the space for keys and data.
• No random limits: cdb handles any database up to 4 gigabytes (or up to an exabyte for cdb64). There are no other restrictions. Records are streamed and don't have to fit into memory. Databases are stored in a machine-independent format (one format for cdb, one format for cdb64).
• Fast atomic database replacement: cdbmake rewrites an entire database much more quickly than other hashing packages. Database replacement is safe against system crashes. Readers don't pause during a rewrite: they continue transparently using the old database until the new database is in place.
• Fast database dumps: cdbdump prints the contents of a database in cdbmake-compatible format.

Latest release: 20251021.

Author

D. J. Bernstein

More support for cdb

More packages saying that they provide tools for you to use cdb format (and in some cases cdb64 format):

• cdb64 from Pierre Carrier: Tweak of cdb-0.75 to support cdb64.
• cdb64-rs from Jiseok Choi: Rust implementation of cdb64, plus wrappers for C, Node.js, and Python.
• CDB_File: from Tim Goodwin, Matt Sergeant, and Todd Rinaldo: Perl wrapper around cdb.
• cdb-full from Kazuteru Okahashi and Rich Lane: Ruby wrapper around cdb.
• CDB::TinyCDB from Alex J. G. Burzyński: Perl wrapper around TinyCDB.
• go-cdb-1: from John Barham: Go implementation.
• go-cdb-2 from Colin Marc: Go implementation.
• go-cdb64 from Chris Lu: Go implementation of cdb64.
• howerj-cdb from Richard James Howe: C implementation.
• hs-cdb from Adam Smith: Haskell implementation.
• libowfat: C implementation from Felix von Leitner (as part of a broader library).
• luacdb from Taj Khattra: Lua wrapper around cdb.
• lua-tinycdb from A. S. Bradbury: Lua wrapper around TinyCDB.
• php-cdb: PHP implementation.
• pure-cdb from Boris Sukholitko: Haskell implementation.
• pycdb from Yusuke Shinyama: Python implementation.
• python-cdb from Mike Pomraning and Alan Grow: Python wrapper around cdb.
• python-pure-cdb from David Wilson: Python implementation. Also supports cdb64.
• rust-cdb from Bruce Guenter: Rust implementation.
• sg-cdb from Michael Alyn Miller: Java implementation.
• swift-cdb: Swift wrapper around howerj-cdb.
• TinyCDB from Michael Tokarev: C implementation.

Examples of applications using cdb format:djbdns.dnsdist.Exim.fastforward.kawipiko.krb5-strength.mess822.Postfix.qconfirm.qmail.ucspi-tcp.

**Version:**This is version 2025.10.23 of the "Intro" web page.