Joomla cache performance with “plain” PHP (no APC)
In this page, we are going to compare the caching impact on Joomla performance when using “plain” PHP (APC was not installed). Which cache type will give us the most pronounced speedup? Lets see...
As you can see, without any cache we have just about 10 pages per second. By enabling the system-wide cache (it can be set in two modes: conservative and progressive) we have a 50% throughput increase. The plugin cache is way faster, outputting more than 35 pages / sec (giving us a 250% increase over no caching).
While throughput (the number of pages / sec) is important, it is not the sole parameter to consider when benchmarking a web server. Another very important thing is the average and maximum web page latency:
The maximum latency decreases significantly but, as it largely depends on the hardware rather than software (eg: a slow disk can lead to very high maximum latency), it remain quite high with all cache types. Average latency however shows a different pattern: if the system-wide cache is not so spectacular, the plugin cache show very good results.
These two tests show that, while any type of caching is desirable, the plugin cache (when usable) is vastly superior to the system-wide one. Moreover, I noticed that the system-wide cache leads to quite high hard-disk usage: in I/O limited systems (a very common scenario), this can be a serious drawback. So, if you notice that the I/O queue of your system is quite high, turning off the system-wide cache can be a good idea.