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MySQL developers have removed the Query Cache feature in the database

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May 31, 2017

We just learned that the developers of the MySQL database have decided its Query Cache feature is more of a bottleneck in some instances and have removed it as of today.

Analyzing the various number of query results and their diversity, if you search for “tuning MySQL query cache” it's not entirely surprising and helps explain the developers' decision to remove the feature.

Of course, the issue here is simply one element: scalability, but it's an important one. As MySQL Server product manager Morgan Tocker has asserted.

The operation of the DB cache looks simple enough. To be sure, SELECT commands are stored in a hash table, and if an incoming query matches the hash, the MySQL server can return the results from the last time the query executed it.

There's an element of protection to prevent the server from returning stale results, as most experienced database admins will tell you.

Tocker asserts that the issue is that the cache “is known not to scale with high-throughput workloads on multi-core machines”.

And even if that problem could be solved, the fix wouldn't make the query cache's performance more predictable, and that's often more important than peak throughput for user-facing systems, he added.

So instead of persisting with fixing the cache per se, MySQL Server's developers have decided “to invest in various improvements that are more generally applicable to all workloads.” The decision makes sense from an engineering point of view.

Database developers and system admins who need DB caching can still use ProxySQL, and other users upgrading to MySQL 8.0 “will be encouraged to use either Server-side Query Rewrite”, Tocker asserted.

Source: The MySQL development team.


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