Shaun, running these commands:
#sysctl vm.dirty_ratio vm.dirty_ratio = 40 # sysctl vm.dirty_background_ratio vm.dirty_background_ratio = 10 shows that these values are even higher by default. When you said RAID buffer size, you meant the controllers cache memory size? Regards, Strahinja On Wed, Oct 10, 2012 at 3:09 PM, Shaun Thomas <stho...@optionshouse.com>wrote: > On 10/10/2012 02:12 AM, Strahinja Kustudić wrote: > > total used free shared buffers cached >> Mem: 96730 96418 311 0 71 93120 >> > > Wow, look at all that RAM. Something nobody has mentioned yet, you'll want > to set some additional kernel parameters for this, to avoid getting > occasional IO storms caused by dirty memory flushes. > > vm.dirty_background_ratio = 1 > vm.dirty_ratio = 5 > > Again, these would go in sysctl.conf, or /etc/sysctl.d/10-dbserver.conf or > something. If you have a newer kernel, look into vm.dirty_background_bytes, > and vm.dirty_bytes. > > The why of this is brought up occasionally here, but it comes down to your > vast amount of memory. The defaults for even late Linux kernels is 5% for > dirty_background_ratio, and 10% for dirty_ratio. So if you multiply it out, > the kernel will allow about 4.8GB of dirty memory before attempting to > flush it to disk. If that number reaches 9.6, the system goes synchronous, > and no other disk writes can take place until *all 9.6GB* is flushed. Even > with a fast disk subsystem, that's a pretty big gulp. > > The idea here is to keep it writing in the background by setting a low > limit, so it never reaches a critical mass that causes it to snowball into > the more dangerous upper limit. If you have a newer kernel, the ability to > set "bytes" is a much more granular knob that can be used to match RAID > buffer sizes. You'll probably want to experiment with this a bit before > committing to a setting. > > > So it did a little swapping, but only minor, still I should probably >> decrease shared_buffers so there is no swapping at all. >> > > Don't worry about that amount of swapping. As others have said here, you > can reduce that to 0, and even then, the OS will still swap something > occasionally. It's really just a hint to the kernel how much swapping you > want to go on, and it's free to ignore it in cases where it knows some data > won't be accessed after initialization or something, so it swaps it out > anyway. > > > -- > Shaun Thomas > OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604 > 312-444-8534 > stho...@optionshouse.com > > ______________________________**________________ > > See > http://www.peak6.com/email_**disclaimer/<http://www.peak6.com/email_disclaimer/>for > terms and conditions related to this email >
