cdb: Intro

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.
krb5-strength.
mess822.
Postfix.
qconfirm.
qmail.
ucspi-tcp.
Examples of comparative benchmarks:
2002.
2004.
2008.
2009.
2014.
2016.

Another spinoff of cdb allowing constant databases beyond 4GB is
Spotify’s sparkey.

Version:
This is version 2025.10.21 of the “Intro” web page.