Genereal advice is to set up shared_buffers to 25% of total RAM. 75% RAM for OS cache. On my case (1.5 TB database, 145 GB RAM), setting shared_buffers bigger than 8GB would give no significant performance impact. On some cases, setting it low would be an advantage http://www.depesz.com/2007/12/05/shared-buffers-and-their-impact-on-performance/
On Tue, Aug 12, 2014 at 10:25 PM, dushy <dushya...@gmail.com> wrote: > Hello all, > > Iam running a postgresql 9.0.13 master/slave instance in a write heavy > workload. > > The hardware is a Dell 720, E5530 - 8 core, 128GB RAM. The database > (around > 250g with indexes/bloat etc) is sitting on flashcache device with 2 fusion- > io PCIe MLC SSDs as frontend and a MD3200 based RAID10 (14*1TB SATA disks) > as backend. OS is centos 6.2 with kernel 2.6.32-431.20.3.el6.x86_64. > > Currently, the performance related configuration is mostly default i,e > shared_buffers, > effective_cache_size. The only directive that seems different is > checkpoint_segments = 96 > > Iam moving to postgresql 9.3 shortly and planning to tune the above > directives as below.. > > effective_cache_size = 100GB # free+buffers is pretty consistent around > 110 > to 120GB and pg_oscache_total is around 80GB > checkpoint_segments = 32 # 96 seems to long and all flushes seem to be > only > due to checkpoint_timeout with the older value > > Additionally iam turning off THB defrag on the OS as suggested by some > posts on the > lists. Though, My initial pgbench testing doesn't seem to indicate any > issues with THB defrag turned on/off. > > Iam not sure about shared_buffers and wal_buffers for this HW/OS & DB > combination - iam inclined to leave > them to defaults. But based on this article > (http://rhaas.blogspot.in/2012/03/tuning-sharedbuffers-and-walbuffers.html > ) > it looks there will be some advantages in tuning it > > What would be a good value (to start with atleast) for shared_buffers and > wal_buffers ? > > Please let me know if additional information will help. > > TIA > dushy > > -- Regards, Soni Maula Harriz
