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
parameters.

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
below.

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.

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
directives.

apc.enabled
boolean

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
commented-out).

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
FAQ. 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
sure.

apc.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.

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.

apc.gc_ttl
integer

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.

apc.filters
string

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.

apc.stat
integer

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
serializer.

apc.include_once_override boolean

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

Warning

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
risk.

apc.rfc1867
boolean

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
previous.

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

Example #1 An apc.rfc1867 example

<?php
print_r(apc_fetch("upload_$_POST[APC_UPLOAD_PROGRESS]"));
?>

The above example will output something similar to:

Array
(
    [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
uploads.

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
to.

apc.localcache.size integer

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

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.

Warning

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

Note:

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
mtime.

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.