Using APC to Speed Up PHP

Introduction

Making PHP run faster is easily accomplished by updating the code or algorithm in use but what if we don't want to fix the code or even look at it? What other options do we have for speeding up our PHP applications?

We've already discussed optimizing LAMP by optimizing MySQL and Apache in Optimizing LAMP: Apache and MySQL.

Install APC

APC is a PHP opcode caching system. This means that when the PHP script is executed and converted to bytecode the intermediary bytecode is cached in APC so that it can simply be looked up next time this line is seen rather than compiling it again.

APC not only provides opcode caching but can also be used as an object cache (similar to Memcached). This object caching requires modifications to the application that wants to utilize it whereas the opcode caching is automatically enabled for all PHP executed while the module is loaded.

To install APC simply install it with your package manager (the package is probably named pecl-apc) or with PECL.

Configuring APC

APC's configuration is in the normal location, /etc/php/apache2-php5/ext-active/apc.ini and usually looks like the following:

extension=apc.so
apc.enabled="1"
apc.shm_segments="4"
apc.shm_size="128"
apc.num_files_hint="1024"
apc.ttl="7200"
apc.user_ttl="7200"
apc.gc_ttl="3600"
apc.cache_by_default="1"
;apc.filters=""
;apc.mmap_file_mask="/tmp/apcphp5.XXXXXX"
apc.slam_defense="0"
apc.file_update_protection="2"
apc.enable_cli="0"
apc.max_file_size="1M"
apc.stat="1"
apc.write_lock="1"
apc.report_autofilter="0"
apc.include_once_override="0"
apc.rfc1867="0"
apc.rfc1867_prefix="upload_"
apc.rfc1867_name="APC_UPLOAD_PROGRESS"
apc.rfc1867_freq="0"
apc.localcache="0"
apc.localcache.size="512"
apc.coredump_unmap="0"

Most of these options can be left with their default values and provide the desired effect.

If you have plenty of available memory on the system utilizing APC you can tweak the following to improve your experiene:

These two parameters dictate the total memory usage for APC. In fact, if you simply multiply these values together you'll get the maximum amount of memory used by APC for the cache.

Caveats

There is a limitation in the kernel on the size of shm files that limits the apc.shm_size. Run the following command to determine this limit for your system:

cat /proc/sys/kernel/shmmax

Conclusion

APC can help you get a bit more performance out of your PHP applications without modifying a line of application code or a lot of configuration. Play with the memory settings to determine what's right for your workload and start serving PHP just a hair faster.