Causes An increase in the ate of fragmentation

If your site does alot of cache_clears you will get more fragmentation. It's not really something this module can help.

Not only that... but if your cache size is too small, you'll end up running out of memory and getting a lot of fragmentation, too. You should only cache small things like cache_bootstrap to start, and keep monitoring (a) fragmentation and (b) the total cache size/usage, and then add another bin, and another, etc.

The facts are;

• add more memory to APC
• [or] filter the files [set] added [cached] to APC cache
• look carefully at the APC TTL times

I give 1024Mb [1Gb] to APC, and for me
about 85Mb is used for the Cached Files [PHP] [daily average]
and about 8Mb is used for the Cached Variables [DATA]
Average Fragmentation: = 0.09%
In my case, with heaps of memory, I cache many Drupal items to APC

      $conf += array(
        'cache_inc'        => './sites/all/modules/cache_backport/cache.inc',
        'cache_backends'   => array('./sites/all/modules/apc/drupal_apc_cache.inc',),
        'apc_show_debug'   => FALSE,
        'page_cache_without_database' => TRUE,
        'page_cache_invoke_hooks'     => FALSE,
        'page_cache_maximum_age'      => 3600,
        'cache_lifetime'              => 0,
        'session_inc'      => './sites/all/modules/cacherouter/session.inc',
            'cache_default_class'               => 'DrupalAPCCache',
            'cache_class_cache'                 => 'DrupalAPCCache',
            'cache_class_cache_block'           => 'DrupalAPCCache',
            'cache_class_cache_bootstrap'       => 'DrupalAPCCache',
            'cache_class_cache_content'         => 'DrupalAPCCache',
            'cache_class_cache_filter'          => 'DrupalAPCCache',
            'cache_class_cache_form'            => 'DrupalAPCCache',
            'cache_class_cache_menu'            => 'DrupalAPCCache',
            'cache_class_cache_page'            => 'DrupalAPCCache',
            'cache_class_cache_pathdst'         => 'DrupalAPCCache',
            'cache_class_cache_pathsrc'         => 'DrupalAPCCache',
            'cache_class_cache_session'         => 'DrupalAPCCache',
            'cache_class_cache_session_user'    => 'DrupalAPCCache',
            'cache_class_cache_update'          => 'DrupalAPCCache',
            'cache_class_cache_users'           => 'DrupalAPCCache',
            'cache_class_cache_views'           => 'DrupalAPCCache',
            'cache_class_cache_views_data'      => 'DrupalAPCCache',
      );

My Linux php.ini (in reference to APC) has the following settings:

[apc]
; Notes: Our 'APC' is STATICALLY compiled into PHP
; ini only settings, all the values here is default unless explained
apc.enabled =                   1
apc.shm_segments =              1
# Notes: Our PHP Max Memory Setting = memory_limit = 512M; we double this
# Old opcodes stay in cache until all old requests satisfied. Leave headroom (up to 2x normal size)
apc.shm_size =                  1024M
# TTL for PHP = 8 hours
apc.ttl =                       28800
# TTL for USER = 4 hours
apc.user_ttl =                  14400
apc.gc_ttl =                    3600
apc.enable_cli =                0
apc.mmap_file_mask =            "/dev/zero"
apc.max_file_size =             4M
# Notes: apc.num_files_hint + apc.user_entries_hint are used by APC to
# help optimize its memory usage when creating the cached memory space
apc.num_files_hint =            2048
apc.user_entries_hint =         8000
# Notes: apc.stat = 0; for production servers: = No disk IO to check if the file has been changed
# With the above we have to restart server to get new (changed) files
# Note: Good to use apc.stat_ctime = 1, if apc.stat = 1
apc.stat =                      1
apc.stat_ctime =                1
apc.slam_defense =              0
apc.write_lock =                1
apc.file_update_protection =    2
apc.rfc1867 =                   1
# Notes: apc.include_once_override = 1; is NOT recommended for PHP 5.3.x+
apc.include_once_override =     0
apc.lazy_classes =              1
apc.lazy_functions =            1
apc.filters =                   ""
apc.cache_by_default  =         1
apc.report_autofilter =         0
apc.localcache =                1
apc.localcache_size =           512
apc.file_md5 =                  1
apc.serializer =                igbinary

[igbinary]
igbinary.compact_strings =      0

APC fragmentation occurs because of:

1. Not enough memory for the APC data footprint
2. [or] excess deletions / purges of cache [data] sets

In some cases, it is better to let the PHP APC TTL purge old data
rather than relying on Drupal [cache] methods.