• Installing/Configuring
  • Runtime Configuration

  • Runtime Configuration
  • Runtime Configuration

    Runtime Configuration

    The behaviour of these functions is affected by
    settings in php.ini.

    Although the default APC settings are fine for many
    installations, serious users should consider tuning the following

    There are two primary decisions to be made
    configuring APC. First, how much memory is going to be allocated to
    APC; and second, whether APC will check if a file has been modified
    on every request. The two ini directives that control these
    settings are apc.shm_size and apc.stat,
    respectively. Read the sections on these two directive carefully

    Once the server is running, the apc.php
    script that is bundled with the extension should be copied
    somewhere into the docroot and viewed with a browser as it provides
    a detailed analysis of the internal workings of APC. If GD is
    enabled in PHP, it will even display some interesting graphs. The
    first thing to ensure, of course, is that it is actually caching
    files. If APC is working, the Cache full count number (on
    the left) will display the number of times the cache has reached
    maximum capacity and has had to forcefully clean any entries that
    haven’t been accessed in the last apc.ttl seconds. This
    number is minimized in a well-configured cache. If the cache is
    constantly being filled, and thusly forcefully freed, the resulting
    churning will have disparaging effects on script performance. The
    easiest way to minimize this number is to allocate more memory for
    APC. Barring that, the apc.filters ought to be used to
    cache fewer scripts.

    When APC is compiled with mmap support (Memory
    Mapping), it will use only one memory segment, unlike when APC is
    built with SHM (SysV Shared Memory) support that uses multiple
    memory segments. MMAP does not have a maximum limit like SHM does
    in /proc/sys/kernel/shmmax. In general MMAP support is
    recommeded because it will reclaim the memory faster when the
    webserver is restarted and all in all reduces memory allocation
    impact at startup.

    APC configuration options
    Name Default Changeable Changelog
    apc.enabled “1” PHP_INI_SYSTEM PHP_INI_SYSTEM in APC 2. PHP_INI_ALL in APC <= 3.0.12.
    apc.shm_segments “1” PHP_INI_SYSTEM  
    apc.shm_size “32M” PHP_INI_SYSTEM  
    apc.shm_strings_buffer “4M” PHP_INI_SYSTEM Available since APC 3.1.4.
    apc.optimization “0” PHP_INI_ALL PHP_INI_SYSTEM in APC 2. Removed in APC 3.0.13.
    apc.num_files_hint “1000” PHP_INI_SYSTEM  
    apc.user_entries_hint “4096” PHP_INI_SYSTEM Available since APC 3.0.0.
    apc.ttl “0” PHP_INI_SYSTEM Available since APC 3.0.0.
    apc.user_ttl “0” PHP_INI_SYSTEM Available since APC 3.0.0.
    apc.gc_ttl “3600” PHP_INI_SYSTEM  
    apc.cache_by_default “1” PHP_INI_ALL PHP_INI_SYSTEM in APC <= 3.0.12. Available since APC
    apc.filters NULL PHP_INI_SYSTEM  
    apc.mmap_file_mask NULL PHP_INI_SYSTEM  
    apc.slam_defense “1” PHP_INI_SYSTEM Available since APC 3.0.0. Prior to APC 3.1.4, the default
    value was “0” (disabled).
    apc.file_update_protection “2” PHP_INI_SYSTEM Available since APC 3.0.6.
    apc.enable_cli “0” PHP_INI_SYSTEM Available since APC 3.0.7.
    apc.max_file_size “1M” PHP_INI_SYSTEM Available since APC 3.0.7.
    apc.use_request_time “1” PHP_INI_ALL Available since APC 3.1.3.
    apc.stat “1” PHP_INI_SYSTEM Available since APC 3.0.10.
    apc.write_lock “1” PHP_INI_SYSTEM Available since APC 3.0.11.
    apc.report_autofilter “0” PHP_INI_SYSTEM Available since APC 3.0.11.
    apc.serializer “default” PHP_INI_SYSTEM Available since APC 3.1.0.
    apc.include_once_override “0” PHP_INI_SYSTEM Available since APC 3.0.12.
    apc.rfc1867 “0” PHP_INI_SYSTEM Available since APC 3.0.13.
    apc.rfc1867_prefix “upload_” PHP_INI_SYSTEM  
    apc.rfc1867_name “APC_UPLOAD_PROGRESS” PHP_INI_SYSTEM  
    apc.rfc1867_freq “0” PHP_INI_SYSTEM  
    apc.rfc1867_ttl “3600” PHP_INI_SYSTEM Available since APC 3.1.1.
    apc.localcache “0” PHP_INI_SYSTEM Available in APC 3.0.14 – 3.1.11.
    apc.localcache.size “512” PHP_INI_SYSTEM vailable in APC 3.0.14 – 3.1.11.
    apc.coredump_unmap “0” PHP_INI_SYSTEM Available since APC 3.0.16.
    apc.stat_ctime “0” PHP_INI_SYSTEM Available since APC 3.0.13.
    apc.preload_path NULL PHP_INI_SYSTEM Available since APC 3.1.1.
    apc.file_md5 “0” PHP_INI_SYSTEM Available since APC 3.1.1.
    apc.canonicalize “1” PHP_INI_SYSTEM Available since APC 3.1.1.
    apc.lazy_functions 0 PHP_INI_SYSTEM Available since APC 3.1.3.
    apc.lazy_classes 0 PHP_INI_SYSTEM Available since APC 3.1.3.

    For further details and definitions of the PHP_INI_* modes, see the
    Where a
    configuration setting may be set

    Here’s a short explanation of the configuration


    apc.enabled can be set to 0 to disable
    APC. This is primarily useful when APC is statically compiled into
    PHP, since there is no other way to disable it (when compiled as a
    DSO, the extension line in php.ini can just be

    apc.shm_segments integer

    The number of shared memory segments to allocate
    for the compiler cache. If APC is running out of shared memory but
    apc.shm_size is set as high as the system allows, raising
    this value might prevent APC from exhausting its memory.

    apc.shm_size string

    The size of each shared memory segment given by a
    shorthand notation as described in this
    . By default, some systems (including most BSD variants)
    have very low limits on the size of a shared memory segment.

    apc.shm_strings_buffer string

    The size of memory to use as a shared buffer for
    strings used internally by APC. Size Should be suffixed by M for
    megabytes, G for gigabytes. Enabling this option will reduce the
    amount of memory used per PHP-FPM worker as strings will be stored
    once rather than for each worker.

    apc.optimization integer

    The optimization level. Zero disables the
    optimizer, and higher values use more aggressive optimizations.
    Expect very modest speed improvements. This is experimental.

    apc.num_files_hint integer

    A “hint” about the number of distinct source files
    that will be included or requested on your web server. Set to zero
    or omit if unsure; this setting is mainly useful for sites that
    have many thousands of source files.

    apc.user_entries_hint integer

    Just like apc.num_files_hint, a “hint” about the number of
    distinct user cache variables to store. Set to zero or omit if not


    The number of seconds a cache entry is allowed to
    idle in a slot in case this cache entry slot is needed by another
    entry. Leaving this at zero means that APC’s cache could
    potentially fill up with stale entries while newer entries won’t be
    cached. In the event of a cache running out of available memory,
    the cache will be completely expunged if ttl is equal to 0.
    Otherwise, if the ttl is greater than 0, APC will attempt to remove
    expired entries.

    apc.user_ttl integer

    The number of seconds a cache entry is allowed to
    idle in a slot in case this cache entry slot is needed by another
    entry. Leaving this at zero means that APC’s cache could
    potentially fill up with stale entries while newer entries won’t be
    cached. In the event of a cache running out of available memory,
    the cache will be completely expunged if ttl is equal to 0.
    Otherwise, if the ttl is greater than 0, APC will attempt to remove
    expired entries.


    The number of seconds that a cache entry may remain
    on the garbage-collection list. This value provides a fail-safe in
    the event that a server process dies while executing a cached
    source file; if that source file is modified, the memory allocated
    for the old version will not be reclaimed until this TTL reached.
    Set to zero to disable this feature.

    apc.cache_by_default boolean

    On by default, but can be set to off and used in
    conjunction with positive apc.filters so that files are
    only cached if matched by a positive filter.


    A comma-separated list of POSIX extended regular
    expressions. If any pattern matches the source filename, the file
    will not be cached. Note that the filename used for matching is the
    one passed to include/require, not the absolute path. If the first
    character of the expression is a + then the expression
    will be additive in the sense that any files matched by the
    expression will be cached, and if the first character is a
    then anything matched will not be cached. The
    case is the default, so it can be left off.

    apc.mmap_file_mask string

    If compiled with MMAP support by using
    –enable-mmap this is the mktemp-style file_mask to pass
    to the mmap module for determining whether your mmap’ed memory
    region is going to be file-backed or shared memory backed. For
    straight file-backed mmap, set it to something like
    /tmp/apc.XXXXXX (exactly 6 Xs). To use
    POSIX-style shm_open/mmap put a .shm somewhere in your
    mask. e.g. /apc.shm.XXXXXX You can also set it to
    /dev/zero to use your kernel’s /dev/zero
    interface to anonymous mmap’ed memory. Leaving it undefined will
    force an anonymous mmap.

    apc.slam_defense integer

    On very busy servers whenever you start the server
    or modify files you can create a race of many processes all trying
    to cache the same file at the same time. This option sets the
    percentage of processes that will skip trying to cache an uncached
    file. Or think of it as the probability of a single process to skip
    caching. For example, setting apc.slam_defense to
    75 would mean that there is a 75% chance that the process
    will not cache an uncached file. So, the higher the setting the
    greater the defense against cache slams. Setting this to 0
    disables this feature.

    Deprecated by apc.write_lock.

    apc.file_update_protection integer

    When a file is modified on a live web server it
    really ought to be done in an atomic manner. That is, written to a
    temporary file and renamed (mv) the file into its
    permanent position when it is ready. Many text editors,
    cp, tar and other such programs don’t do this. This
    means that there is a chance that a file is accessed (and cached)
    while it is still being written to. This
    apc.file_update_protection setting puts a delay on caching
    brand new files. The default is 2 seconds, which means that if the
    modification timestamp (mtime) on a file shows that it is
    less than 2 seconds old when it is accessed, it will not be cached.
    The unfortunate person who accessed this half-written file will
    still see weirdness, but at least it won’t persist. If all of the
    webserver’s files are atomically updated, via some method like
    rsync (which updates correctly),
    this protection can be disabled by setting this directive to 0. If
    the system is flooded with i/o and some update procedures are
    taking longer than 2 seconds, this setting should be increased to
    enable the protection on those slower update operations.

    apc.enable_cli integer

    Mostly for testing and debugging. Setting this
    enables APC for the CLI version of PHP. Under normal circumstances,
    it is not ideal to create, populate and destroy the APC cache on
    every CLI request, but for various test scenarios it is useful to
    be able to enable APC for the CLI version of PHP easily.

    apc.max_file_size integer

    Prevent files larger than this value from getting
    cached. Defaults to 1M.


    Be careful changing this setting. This defaults to
    on, forcing APC to stat (check) the script on each request to
    determine if it has been modified. If it has been modified it will
    recompile and cache the new version. If this setting is off, APC
    will not check, which usually means that to force APC to recheck
    files, the web server will have to be restarted or the cache will
    have to be manually cleared. Note that FastCGI web server
    configurations may not clear the cache on restart. On a production
    server where the script files rarely change, a significant
    performance boost can be achieved by disabled stats.

    For included/required files this option applies as
    well, but note that for relative path includes (any path that
    doesn’t start with / on Unix) APC has to check in order to uniquely
    identify the file. If you use absolute path includes APC can skip
    the stat and use that absolute path as the unique identifier for
    the file.

    apc.write_lock boolean

    On busy servers, when the web server is first
    started, or when many files have been modified at the same time,
    APC may try to compile and cache the same file multiple times.
    Write_lock guarantees that only one process will attempt to compile
    and cache an uncached script. The other processes attempting to use
    the script will run without using the opcode cache, rather than
    locking and waiting for the cache to prime.

    apc.report_autofilter boolean

    Logs any scripts that were automatically excluded
    from being cached due to early/late binding issues.

    apc.serializer string

    Used to configure APC to use a third party

    apc.include_once_override boolean

    Optimize include_once and require_once calls and avoid the expensive
    system calls used.


    This feature is EXPERIMENTAL. The behaviour of this directive, its
    name, and surrounding documentation may change without notice in a
    future release of APC. This feature should be used at your own


    RFC1867 File Upload Progress hook handler is only
    available if APC was compiled against PHP 5.2.0 or later. When
    enabled, any file uploads which includes a field called
    APC_UPLOAD_PROGRESS before the file field in an upload
    form will cause APC to automatically create an upload_key user cache entry where key is the value of the
    APC_UPLOAD_PROGRESS form entry.

    Note that the hidden field specified by
    APC_UPLOAD_PROGRESS must come before the file field,
    otherwise the upload progress will not work correctly.

    Note that the file upload tracking is not
    threadsafe at this point, so new uploads that happen while a
    previous one is still going will disable the tracking for the

    Note that the rate is only available once
    all file transfers are completed.

    Example #1 An apc.rfc1867 example


    The above example will output something similar to:

        [total] => 1142543
        [current] => 1142543
        [rate] => 1828068.8
        [filename] => test
        [name] => file
        [temp_filename] => /tmp/php8F
        [cancel_upload] => 0
        [done] => 1
    apc.rfc1867_prefix string

    Key prefix to use for the user cache entry
    generated by rfc1867 upload progress functionality.

    apc.rfc1867_name string

    Specify the hidden form entry name that activates
    APC upload progress and specifies the user cache key suffix.

    apc.rfc1867_freq string

    The frequency that updates should be made to the
    user cache entry for upload progress. This can take the form of a
    percentage of the total file size or a size in bytes optionally
    suffixed with “k”, “m”, or “g” for
    kilobytes, megabytes, or gigabytes respectively (case insensitive).
    A setting of 0 updates as often as possible, which may cause slower

    apc.rfc1867_ttl integer

    TTL for rfc1867 entries.

    apc.localcache boolean

    This enables a lock-free local process shadow-cache
    which reduces lock contention when the cache is being written

    apc.localcache.size integer

    The size of the local process shadow-cache, should
    be set to a sufficiently large value, approximately half of

    apc.coredump_unmap boolean

    Enables APC handling of signals, such as SIGSEGV,
    that write core files when signaled. When these signals are
    received, APC will attempt to unmap the shared memory segment in
    order to exclude it from the core file. This setting may improve
    system stability when fatal signals are received and a large APC
    shared memory segment is configured.


    This feature is potentially dangerous. Unmapping
    the shared memory segment in a fatal signal handler may cause
    undefined behaviour if a fatal error occurs.


    Although some kernels may provide a facility to
    ignore various types of shared memory when generating a core dump
    file, these implementations may also ignore important shared memory
    segments such as the Apache scoreboard.

    apc.stat_ctime integer

    Verification with ctime will avoid problems caused
    by programs such as svn or rsync by making sure inodes haven’t
    changed since the last stat. APC will normally only check

    apc.canonicalize bool

    If on, then relative paths are canonicalized in
    no-stat mode. If set, then files included via stream wrappers can
    not be cached as realpath()
    does not support stream wrappers.

    apc.preload_path string

    Optionally, set a path to the directory that APC
    will load cache data at startup.

    apc.use_request_time bool

    Use the SAPI request
    start time for TTL.

    apc.file_md5 bool

    Records a md5 hash of files.

    apc.lazy_functions integer

    Enables lazy loading for functions.

    apc.lazy_classes integer

    Enables lazy loading for classes.