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

How to change MySQL account passwords with no downtime

How to change MySQL account passwords with no downtime

Changing the password of a MySQL account that an application uses was hard before MySQL 8.0. It is easy in MySQL 8.0 and later, thanks to two clauses of ALTER USER: RETAIN CURRENT PASSWORD and DISCARD OLD PASSWORD.

Read more
Six connections and a long queue: how a TLS-inspecting proxy quietly turned HTTP/2 into HTTP/1.1

Six connections and a long queue: how a TLS-inspecting proxy quietly turned HTTP/2 into HTTP/1.1

I recently tracked down a performance problem that turned out not to be in the application, the servers, or the CDN. A corporate TLS-inspecting proxy sat between the users and the site.

Read more
How easy is it to use the VillageSQL MCP extension?

How easy is it to use the VillageSQL MCP extension?

VillageSQL published Access MySQL over MCP with vsql-mcp . The extension serves the Model Context Protocol from inside the database, so an agent talks to MySQL over Streamable HTTP without a sidecar holding a credential.

Read more