I set:
shared_buffers = 4GB
effective_cache_size = 72GB
work_mem = 128MB
maintenance_work_mem = 4GB
checkpoint_segments = 64
checkpoint_completion_target = 0.9
random_page_cost = 3.5
cpu_tuple_cost = 0.05
Where can I get the values for random_page_cost and for cpu_tuple_cost where they depend on hardware? I know that for SSDs random_page_cost should be 1.0, but I have no idea what value this should be for different types of drives.
I also set:
vm.swappiness = 0
vm.overcommit_memory = 2
vm.overcommit_ratio = 50
But I don't understand why do I need to set overcommit_memory, since I only have postgres running, nothing else would allocate memory anyway?
I will set readahead later, first I want to see how is this working.
Strahinja Kustudić | System Engineer | Nordeus
On Wed, Oct 10, 2012 at 10:52 AM, Julien Cigar <jcigar@xxxxxxxxx> wrote:
On 10/10/2012 10:30, Strahinja Kustudić wrote:also with 15k SCSI you can reduce random_page_cost to 3.5 (instead of 4.0)Thanks for very fast replies everyone :)
@Laurenz I know that effective cache size is only used for the query planner, what I was saying is that if I tell it that it can have 90GB cached items, that is not trues, since the OS and Postgres process itself can take more than 6GB, which would mean 90GB is not the correct value, but if effective_cache size should be shared_buffers+page cache as Tomas said, than 90GB, won't be a problem.
@Tomas here are the values:
# cat /proc/sys/vm/swappiness
60
# cat /proc/sys/vm/overcommit_memory
0
# cat /proc/sys/vm/overcommit_ratio
50
I will turn of swappiness, I was meaning to do that, but I don't know much about the overcommit settings, I will read what they do.
@Julien thanks for the suggestions, I will tweak them like you suggested.
I also recommend to raise cpu_tuple_cost to 0.05 (instead of 0.01), set vm.swappiness to 0, vm.overcommit_memory to 2, and finally raise the read-ahead (something like 8192)
Strahinja Kustudić | System Engineer | Nordeus
On Wed, Oct 10, 2012 at 10:11 AM, Julien Cigar <jcigar@xxxxxxxxx> wrote:
On 10/10/2012 09:12, Strahinja Kustudić wrote:Hello,
Hi everyone,
Generally going over 4GB for shared_buffers doesn't help.. some of the overhead of bgwriter and checkpoints is more or less linear in the size of shared_buffers ..
I have a Postgresql 9.1 dedicated server with 16 cores, 96GB RAM and RAID10 15K SCSI drives which is runing Centos 6.2 x64. This server is mainly used for inserting/updating large amounts of data via copy/insert/update commands, and seldom for running select queries.
Here are the relevant configuration parameters I changed:
shared_buffers = 10GB
effective_cache_size = 90GB
effective_cache_size should be ~75% of the RAM (if it's a dedicated server)
work_mem = 32MB
with 96GB of RAM I would raise default work_mem to something like 128MB
maintenance_work_mem = 512MB
again, with 96GB of ram you can raise maintenance_work_mem to something like 4GBJulien
checkpoint_segments = 64
checkpoint_completion_target = 0.8
My biggest concern are shared_buffers and effective_cache_size, should I increase shared_buffers and decrease effective_cache_size? I read that values above 10GB for shared_buffers give lower performance, than smaller amounts?
free is currently reporting (during the loading of data):
$ free -m
total used free shared buffers cached
Mem: 96730 96418 311 0 71 93120
-/+ buffers/cache: 3227 93502
Swap: 21000 51 20949
So it did a little swapping, but only minor, still I should probably decrease shared_buffers so there is no swapping at all.
Thanks in advance,
Strahinja
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