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The ccache Utility

There’s a very useful tool for gcc and similar compilers called ccache which many people may not be aware is installed on their system. It is a compiler cache. Supported languages include C, C++, Objective-C and Objective-C++. The idea behind ccache is to speed up code recompilation by caching the result of previous compilations and detecting when the same compilation is being done again. While it may take a few seconds longer to compile a program the first time you use ccache, subsequent compiles will typically be much faster.

Here is what my ccache cache statistics look like after a few months of compiling various applications:

$ ccache -s
cache directory                     /home/fpm/.ccache
cache hit (direct)                  5649
cache hit (preprocessed)             383
cache miss                         27404
called for link                     5017
called for preprocessing            1805
multiple source files                  7
compile failed                       465
preprocessor error                   164
bad compiler arguments               407
unsupported source language           31
autoconf compile/link               3229
unsupported compiler option            3
no input file                       1498
files in cache                     26626
cache size                         924.6 Mbytes
max cache size                       1.0 Gbytes

$ cd ~/.ccache
$ ls -al
total 80
drwxrwxr-x 19 fpm fpm 4096 Jun 30  2012 .
drwxr-xr-x 49 fpm fpm 4096 Mar 14 03:01 ..
drwxrwxr-x 18 fpm fpm 4096 Jan 30 21:09 0
drwxrwxr-x 18 fpm fpm 4096 Jan 30 21:09 1
drwxrwxr-x 18 fpm fpm 4096 Jan 30 21:09 2
drwxrwxr-x 18 fpm fpm 4096 Jan 30 21:09 3
drwxrwxr-x 18 fpm fpm 4096 Jan 30 21:09 4
drwxrwxr-x 18 fpm fpm 4096 Jan 30 21:09 5
drwxrwxr-x 18 fpm fpm 4096 Jan 30 21:09 6
drwxrwxr-x 18 fpm fpm 4096 Mar  4 10:58 7
drwxrwxr-x 18 fpm fpm 4096 Mar  4 10:58 8
drwxrwxr-x 18 fpm fpm 4096 Mar  4 10:58 9
drwxrwxr-x 18 fpm fpm 4096 Jan 30 21:09 a
drwxrwxr-x 18 fpm fpm 4096 Jan 30 21:09 b
drwxrwxr-x 18 fpm fpm 4096 Jan 30 21:09 c
-rw-rw-r--  1 fpm fpm  190 Jun 18  2012 CACHEDIR.TAG
drwxrwxr-x 18 fpm fpm 4096 Mar  4 10:58 d
drwxrwxr-x 18 fpm fpm 4096 Jan 30 21:09 e
drwxrwxr-x 18 fpm fpm 4096 Mar  4 10:58 f
drwxrwxr-x  2 fpm fpm 4096 Jan 30 21:09 tmp
$

$ cd f/f
$ ls -l
total 2148
-rw-rw-r-- 1 fpm fpm   6435 Nov  2 18:21 0a632930c6b3a5e0b23bd1b4ebca1e-82602.manifest
-rw-rw-r-- 1 fpm fpm  33830 Nov  2 15:29 0b3cef8ce8e69c25b4d1f26c401896-36044.manifest
-rw-rw-r-- 1 fpm fpm   4270 Nov  2 16:06 0ce14408ae925b994b8d9c54b28f75-50633.d
-rw-rw-r-- 1 fpm fpm    945 Nov  2 16:06 0ce14408ae925b994b8d9c54b28f75-50633.o
-rw-rw-r-- 1 fpm fpm  10372 Nov  2 18:20 1172b26ad90ba289c5715ea597237e-386743.d
-rw-rw-r-- 1 fpm fpm  16368 Nov  2 18:20 1172b26ad90ba289c5715ea597237e-386743.o
-rw-rw-r-- 1 fpm fpm  27240 Jan 30 21:09 1270a4dd79671332c60f531bf56360-111704.o
-rw-rw-r-- 1 fpm fpm  61706 Nov  2 15:03 13a8ecc043d194fee1f721a9702dff-2694676.d
-rw-rw-r-- 1 fpm fpm  15520 Nov  2 15:03 13a8ecc043d194fee1f721a9702dff-2694676.o
-rw-rw-r-- 1 fpm fpm  40310 Nov  2 14:29 1f37e26f195d6a0a69d4e0428f67b5-1100836.d
-rw-rw-r-- 1 fpm fpm 104424 Nov  2 14:29 1f37e26f195d6a0a69d4e0428f67b5-1100836.o
-rw-rw-r-- 1 fpm fpm  13720 Jan 30 21:09 28a55ea10e58a91ac40f7b4ab97822-82191.o
-rw-rw-r-- 1 fpm fpm   1240 Nov  2 17:27 34197bcdb4d8671f13ed9b9cab0658-256.o
-rw-rw-r-- 1 fpm fpm  54539 Nov  2 15:42 3ba24e8b3ea4aee5e0d1311a024c0d-2422333.d
-rw-rw-r-- 1 fpm fpm  24680 Nov  2 15:42 3ba24e8b3ea4aee5e0d1311a024c0d-2422333.o
...


You can clear out the ccache cache as follows:

$ ccache -C
Cleared cache
[fpm@ultra f]$ ccache -s
cache directory                     /home/fpm/.ccache
cache hit (direct)                  5649
cache hit (preprocessed)             383
cache miss                         27404
called for link                     5017
called for preprocessing            1805
multiple source files                  7
compile failed                       465
preprocessor error                   164
bad compiler arguments               407
unsupported source language           31
autoconf compile/link               3229
unsupported compiler option            3
no input file                       1498
files in cache                         0
cache size                             0 Kbytes
max cache size                       1.0 Gbytes
$


You can also reduce the maximum size of the ccache cache:

$ ccache -M 500M
Set cache size limit to 500.0 Mbytes
$


Fedora by default seems to allocate 1Gb of ccache cache space.

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