Mysql slave invalidating query cache entries table
The query cache has been disabled-by-default since My SQL 5.6 (2013) as it is known to not scale with high-throughput workloads on multi-core machines.Rene confirmed this in his post yesterday, but it has also previously been mentioned by Stewart Smith, Domas Mituzas (update: and Kristian Koehntopp).We can use the data we got in the request and / or simply query a master node and cache the results.Then when a user is redirected to the page with the updated content — instead of getting a miss from the cache (that would force us to fetch data from the database and risk hitting the replication lag) — we actually get the up-to-date entry from the warm cache.
Before we get to the subject of today’s post, let me start with an introduction. It compares incoming queries that start with The ideal scenario for the query cache tends to be largely read-only, where there are a number of very expensive queries which examine millions of rows only to return a few.Your app can survive one slave node going down and still serve the traffic.Having a strong dependency on a master node (that you cannot scale by simply adding more masters) for your read-only requests is a risky game., mostly INSERT statements, around 5-10 rows per second. In 5-10 seconds when it will be time to process new data again the same lock up will happen. Query #2 is the updating of the post-processed data.A PHP based application is running on the server that reads the freshly replicated data every 5-10 seconds, processes it and stores (INSERT ON DUPLICATE KEY UPDATE) results in a separate database . A web application displays the post-processed data for the user. Query #3 is streaming (unbuffered) the newly replicated data for processing.
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We used this approach to improve the behaviour of the code that was responsible for 21% of database queries that were made to a master node when handling GET requests (for instance when viewing a wiki article). A similar fix was applied to a code that was handling talk page edits notifications.