After reading several articles on the performance drag that Linux atime has on file systems we would like to mount our DB volumes with the noatime parameter to see just what type of a performance gain we will achieve. Does PostgreSQL use atime in any way when reading/writing data? If we turn off/disable atime on the DB volumes will that cause any type of issue at all with PostgreSQL 8.1 on Red Hat Enterprise Linux?
Ingo Molnar who is the real-time/performance guru of the Linux Kernel wrote "I cannot over-emphasize how much of a deal it is in practice. Atime updates are by far the biggest IO performance deficiency that Linux has today. Getting rid of atime updates would give us more everyday Linux performance than all the page cache speedups of the past 10 years, _combined_".
The atime is updated (synchronously) for queries as well as updates/inserts whereas logs/journals are only updated (synchronously) for the updates/inserts... This is true for every read -- even if it is page by page -- each page request causes a synchronous atime update.
http://kerneltrap.org/node/14148
Thanks,
Keaton
