Right now there is a discussion on Planet MySQL regarding MySQL / Linux swap problem. Peter Zaitsev originally brought the problem of MySQL swapping to light. Recently, Dathan Pattishall also wrote about it in his post Linux 64-bit, MySQL, Swap and Memory. Don McAskill followed up with his post, MySQL and the Linux Swap problem, and an interesting way to get around the issue: "make swap partitions out of RAM disks." Don also points to another article by Kevin regarding using O_DIRECT to fix the swap issue.
To get to the point, some time ago, I experienced a similar issue on few of my old servers running Solaris V210, UFS with plenty of memory available. My initial thinking was that I am experiencing similar issue so during my presentation at MySQL Conference, Optimizing MySQL and InnoDB on Solaris 10, I pointed that this *may* exist in Solaris 10. Luckily a Sun representative (I believe it was Matt Ingenthron) corrected me towards the end of my session and pointed that UFS and Solaris 10 kernel have features built to avoid just that. That confirmation from a Sun representative was authoritative. We have already decommissioned the affected servers from production so it may be some time before I can find the precise reason why we experienced the swapping issue. Note that I haven't seen this issue on any of our other V210, V440 and T5120s in production.
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