On 4.4.2012 18:22, Scott Marlowe wrote: > On Wed, Apr 4, 2012 at 7:20 AM, Tomas Vondra <tv@xxxxxxxx> wrote: >> On 4.4.2012 15:15, Scott Marlowe wrote: >>> On Wed, Apr 4, 2012 at 3:42 AM, Cesar Martin <cmartinp@xxxxxxxxx> wrote: >>>> >>>> I have noticed that since I changed the setting vm.zone_reclaim_mode = 0, >>>> swap is totally full. Do you recommend me disable swap? >>> >>> Yes >> >> Careful about that - it depends on how you disable it. >> >> Setting 'vm.swappiness = 0' is a good idea, don't remove the swap (I've >> been bitten by the vm.overcommit=2 without a swap repeatedly). > > I've had far more problems with swap on and swappiness set to 0 than > with swap off. But this has always been on large memory machines with > 64 to 256G memory. Even with fairly late model linux kernels (i.e. > 10.04 LTS through 11.04) I've watched the kswapd start up swapping > hard on a machine with zero memory pressure and no need for swap. > Took about 2 weeks of hard running before kswapd decided to act > pathological. > > Seen it with swap on, with swappiness to 0, and overcommit to either 0 > or 2 on big machines. Once we just took the swap partitions away it > the machines ran fine. I've experienced the issues in exactly the opposite case - machines with very little memory (like a VPS with 512MB of RAM). I did want to operate that machine without a swap yet it kept failing because of OOM errors or panicking (depending on the overcommit ratio value). Turns out it's quite difficult (~ almost impossible) tune the VM for a swap-less case. In the end I've just added a 256MB of swap and everything started to work fine - funny thing is the swap is not used at all (according to sar). T. -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
