vmod-cachehits

SYNOPSIS

import cachehits;

DESCRIPTION

Varnish vmod to enable hinting to the backend the number of previous cache hits.

The intended usage is for the backend to notice that an object has a high cache hit rate and run additional optimizations. (for example, higher png compression level)

FUNCTIONS

Prototype

count()

Return value

INT

Description

Returns number of cache hits for stale object

CacheHits

set bereq.http.Cache-Hits = cachehits.count();

INSTALLATION

The source tree is based on autotools to configure the building, and does also have the necessary bits in place to do functional unit tests using the varnishtest tool.

Building requires the Varnish header files and uses pkg-config to find the necessary paths.

Usage:

./autogen.sh
./configure

If you have installed Varnish to a non-standard directory, call autogen.sh and configure with PKG_CONFIG_PATH pointing to the appropriate path. For instance, when varnishd configure was called with --prefix=$PREFIX, use

export PKG_CONFIG_PATH=${PREFIX}/lib/pkgconfig
export ACLOCAL_PATH=${PREFIX}/share/aclocal

The module will inherit its prefix from Varnish, unless you specify a different --prefix when running the configure script for this module.

Make targets:

• make - builds the vmod.
• make install - installs your vmod.
• make check - runs the unit tests in src/tests/*.vtc.
• make distcheck - run check and prepare a tarball of the vmod.

If you build a dist tarball, you don't need any of the autotools or pkg-config. You can build the module simply by running:

./configure
make

Installation directories

By default, the vmod configure script installs the built vmod in the directory relevant to the prefix. The vmod installation directory can be overridden by passing the vmoddir variable to make install.

USAGE

In your VCL you could then use this vmod along the following lines:

import cachehits;

sub vcl_backend_fetch {
        set bereq.http.Cache-Hits = cachehits.count();
}

COMMON PROBLEMS

• configure: error: Need varnish.m4 -- see README.rst

  Check whether PKG_CONFIG_PATH and ACLOCAL_PATH were set correctly before calling autogen.sh and configure

• Incompatibilities with different Varnish Cache versions

  Make sure you build this vmod against its correspondent Varnish Cache version. For instance, to build against Varnish Cache 4.1, this vmod must be built from branch 4.1.