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.
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.
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.