Archive for the ‘Geek’ Category
Table statistics draft 2, the slow query log
I’ve posted a new table statistics patch which is the next version of the session table/index statistics patch This version of the patch adds slow query log output. If a query is logged to the slow query log it will have row count statistics added to it.
I’m not sure about the format of the [...]
First draft of per session table and index statistics
I had some free time over Thanksgiving so I decided to work on something I have been thinking about for quite some time. I hacked up Google’s show table_statistics patch to also track stats per connection. I say this is a first draft hack because I based it off of the v2 patch which [...]
pid file directory and a full disk
To continue the pid file theme I’ve found another slight issue. This was unrelated to the testing which I found the previous pid file issues. I was working on an unmonitored development mysql system. While working on it I ran it out of disk space in /. The box has it’s mysql datadir in a [...]
Attempting to unwind the tangled web of pid file creation.
Previously I wrote about how late the mysql pid file is created in the startup process. At first glance it seemed like a relatively easy thing to fix. In main() there is a call to start_signal_handler(). The first instance of static void start_signal_handler() does only one thing. It checks !opt_bootstrap to make sure mysqld isn’t [...]
mysqld_safe and pid file creation race condition
mysql_safe is responsible for restarting mysqld if it crashes and will exit cleanly if mysqld was shutdown. The way it determines if mysqld shutdown correctly is if the pid file is cleaned up correctly. MySQL does quite a few things before creating the pid file like initializing storage engines. It can take quite a while [...]
InnoDB Deadlock Count Patch
InnoDB Deadlock Count Patch
Deadlocks are a common occurrence in relational databases. They usually aren’t a problem until they start happening too frequently. Innodb can provide you with information about the latest deadlock in SHOW ENGINE INNODB STATUS. This can be useful for debugging but it’s almost impossible to get the rate at which deadlocks are [...]
Default log file name changes and replication breakage.
In a Great Magnet moment Trent Lloyd posted an excellent write-up on how to recover from relay log name changes on the same day I was going to write up a procedure to send to a client who had a similar issue. Thanks Trent! The problem goes a bit deeper than server hostname changes because [...]
cinfo for seeing how much of a file is being cached
cinfo is a kick ass program written by the author of PowerDNS Bert Hubert to show how much of a file is being cached by the operating system. It’s great for testing to see if myisam data files are being read from the operating system cache or off disk. For example this is the cache [...]
Load average
Modern operating systems give the impression of running more processes than the number of available processors by giving each process that wants to run, such as your web browser or text editor a tiny slice of time in which they can execute. By switching out the running process very quickly it looks as though all [...]
fadvise syscall, myisam data file caching, and a lesson learned in debugging
fadvise is a system call that can be used to give Linux hints about how it should be caching files. It has a few options for caching, not caching, read ahead, and random access. I was looking into used fadvise because a client ran into an issue where some infrequently used myisam data files were [...]