How to find configuration file MySQL uses?
A customer called me today asking for help with locating the configuration file used by one of their production MySQL instances. From the description I was given it appeared that their server had at...
View ArticleCan COUNT(*) be used in MySQL on InnoDB tables?
COUNT() function returns a number of rows returned by a query. In a popular opinion COUNT(*) should not be used on InnoDB tables, but this is only half true. If a query performs filtering on any...
View ArticleHow to resize InnoDB logs?
If for any reason you need to change the size of InnoDB log files (also known as transaction logs), but not sure how to do it, this post will guide you through the steps. Step 1: Preflight checks...
View ArticleHow to selectively kill queries in MySQL?
For as long as it is only about a few of them, it is as simple as looking at the SHOW PROCESSLIST output for thread identifiers to kill. They can be found in the first column called Id. These values...
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What is the proper size of InnoDB logs?
In one of my previous posts, “How to resize InnoDB logs?”, I gave the advice on how to safely change the size of transaction logs. This time, I will explain why doing it may become necessary. A brief...
View ArticleHow to check if MySQL has been swapped out?
How to check if any MySQL memory has been swapped out? This post explains it. Check if system is currently using any swap: server ~ # free -m total used free shared buffers cached Mem: 3954 2198 1755 0...
View ArticleDedicated table for counters
There are a few ways to implement counters. Even though it’s not a complex feature, often I see people having problems around it. This post describes how bad implementation can impact both application...
View ArticleWhy do threads sometimes stay in ‘killed’ state in MySQL?
Have you ever tried to kill a query, but rather than just go away, it remained among the running ones for an extended period of time? Or perhaps you have noticed some threads makred with killed showing...
View ArticleMySQL, OOM Killer, and everything related
Do the operating systems kill your MySQL instances from time to time? Are some database servers swapping constantly? These are relatively common problems. Why? How to prevent them? Memory allocation...
View ArticleA security flaw in MySQL authentication. Is your system vulnerable?
A few days ago Sergei Golubchik of Monty Program sent an e-mail to the Open Source Security mailing list informing about a security vulnerability in MySQL authentication system. Under certain...
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