query_cache_size=0 is not enough

Last week at the OUG Harmony conference thanks to Dimitri Kravtchuk I learned that setting query_cache_size=0 does not disable and remove locking from the Query Cache. You actually need to also set query_cache_type=0. This appears to been a bug, seen in the presently still open MySQL bugs database entry #38511 .

My recommendation to customers now is to set both variables on all existing MySQL versions if you are not using the MySQL Query Cache.

Thanks to the Performance Schema in MySQL 5.5 for uncovering this. More information in Dimitri’s detailed post at MySQL Performance: Using Performance Schema

Details of all MySQL presentations at OUG Harmony 2011 in Helsinki, Finland.

Tagged with: Databases MySQL

Related Posts

My take on PyCon Australia 2026

My take on PyCon Australia 2026

PyCon AU 2026 held in Brisbane this week was a five day event for the Python community. With specialized tracks and dedicated tutorial and engineering days there was a wide variety of content available.

Read more
Fixing Old Software Bugs Without Thinking

Fixing Old Software Bugs Without Thinking

I previously came across an issue in my benchmarking work where I relied on the Latency Histogram section of sysbench output. On Linux it worked fine — I generally ran my workload there, so it never mattered.

Read more
Curating DuckDB Datasets Leveraging AI

Curating DuckDB Datasets Leveraging AI

In Curated MySQL Data Sets for Realistic Testing I described datasets assembled the manual way — download, schema, load, validate, document — over hours or days per source. This post is the follow-up I promised: what changes when AI assists the same workflow, using DuckDB as the target engine and GeoNames as the first example.

Read more