Fast Web log analyzer using probabilistic data structures
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Logswan Build Status Coverity Scan Build Status

Logswan is a fast Web log analyzer using probabilistic data structures. It is targeted at very large log files, typically APIs logs. It has constant memory usage regardless of the log file size, and takes approximatively 4MB of RAM.

Unique visitors counting is performed using two HyperLogLog counters (one for IPv4, and another one for IPv6), providing a relative accuracy of 0.10%. String representations of IP addresses are used and preferred as they offer better precision.

Project design goals include: speed, memory-usage efficiency, and keeping the code as simple as possible.

Logswan is opinionated software:

  • It only supports the Common Log Format, in order to keep the parsing code simple. It can of course process the Combined Log Format as well (referer and user agent fields will be discarded)
  • It does not split results per day, but log files can be split prior to being processed
  • Input file size and bandwidth usage are reported in bytes, there are no plans to format or round them


Currently implemented features:

  • Counting bandwidth used
  • Counting number of processed lines / invalid lines
  • Counting number of hits (IPv4 and IPv6 hits)
  • Counting visits (unique IP addresses for both IPv4 and IPv6)
  • GeoIP lookups (for both IPv4 and IPv6)
  • Hourly hits distribution
  • HTTP method distribution
  • HTTP protocol (HTTP/1.0 or HTTP/1.1) distribution
  • HTTP status codes distribution


Logswan uses the CMake build system and requires Jansson and libmaxminddb libraries and header files.

Installing dependencies

  • OpenBSD: pkg_add -r cmake jansson libmaxminddb
  • Mac OS X: brew install cmake jansson libmaxminddb
  • Alpine Linux: apk add cmake gcc make musl-dev jansson-dev libmaxminddb-dev
  • Debian / Ubuntu: apt-get install build-essential cmake libjansson-dev libmaxminddb-dev


cmake .

Logswan has been sucessfully compiled and tested on Mac OS X, OpenBSD, NetBSD, and Linux with both Clang and GCC.


Logswan packages are available for:


pkg_add logswan

Pkgsrc (NetBSD, SmartOS, Mac OS X, etc.)

pkgin install logswan

GeoIP2 databases

Logswan looks for GeoIP2 databases in ${CMAKE_INSTALL_PREFIX}/share/GeoIP2 by default, which points to /usr/local/share/GeoIP2.

A custom directory can be set using the GEOIP2DIR variable when invoking CMake:

cmake -DGEOIP2DIR=/var/db/GeoIP .

The free GeoLite2 databases from MaxMind can be downloaded here:


logswan [-ghv] file

If file is a single dash (`-'), logswan reads from the standard input.

Options are:

-g Enable GeoIP lookups
-h Display usage
-v Display version

Logswan outputs JSON data to stdout.

Measuring Logswan memory usage

Heap profiling can be done using valgrind, as follows:

valgrind --tool=massif logswan access.log
ms_print massif.out.*


Logswan is released under the BSD 2-Clause license. See LICENSE file for details.


Logswan is developed by Frederic Cambus.


Project homepage: