Query Cache Contention

oss-performance is a Hack language script which controls the operation of nginx, siege, and a specified PHP or HHVM runtime using MariaDB.

It performs the following steps:
Installs the workload (from an included archive)
Starts nginx, Initializes the PHP engine, Performs a sanity check
Runs 200 sequential requests with siege (single threaded warmup)
Runs siege for a 60 second multi-threaded warmup
Benchmarks with siege for 60 seconds of multi-threaded access
Tears down nginx and PHP
Prints results
Install from link OSS-performance

When the Query Cache is enabled, we see very low CPU utilization and in the mariadb shell we see (using show processlist that they are waiting on the query cache.

We disabled the Query Cache and are able to saturate the CPU and also doubled the performance.