MySQL 5.5.40 was recently released (it is the latest MySQL 5.5, is GA), and is available for download here:

http://dev.mysql.com/downloads/mysql/5.5.html

This release, similar to the last 5.5 release, is mostly uneventful.

There were 0 “Functionality Added or Changed” bugs this time, and 18 bugs overall fixed.

Out of the 18 bugs, most seemed rather minor or obscure, but there are 3 I think are worth noting (all 3 are InnoDB-related, regressions, and serious if you encounter them, so best to be aware of them):

• InnoDB: An ALTER TABLE … ADD FOREIGN KEY operation could cause a serious error. (Bug #19471516, Bug #73650)
• InnoDB: With a transaction isolation level less than or equal to READ COMMITTED, gap locks …

Do you know if your production MySQL servers will come back up when restarted? A recent support episode illustrates a number of best practices. The task looked trivial: Update a production MySQL server (replication master) with a configuration tuned and tested on a development server. Clean shutdown, change configuration, restart. Unfortunately, the MySQL daemon did not just ‘come back’, leaving 2 sites offline. Thus begins an illuminating debugging story. First place to look is the daemon error log, which revealed that the server was segfaulting, seemingly at the end of or just after InnoDB recovery. Reverting to the previous configuration did not help, nor did changing the InnoDB recovery mode. Working with the client, we performed a failover to a replication slave, while I got a second opinion from a fellow engineer to work out what had gone wrong on the server. Since debug symbols weren’t shown in the stack trace, we needed …