Re: Postgresql 9.3 tuning advice

[Soni M <diptatapa@xxxxxxxxx>]

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 <dushyanth@xxxxxxxxx> 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