Tuning for PostGreSQL Database
cweimann at k12hq.com
Fri Jul 25 09:26:07 PDT 2003
On Fri 07/25/2003-12:03:32AM -0700, Tom Samplonius wrote:
> Maybe you should continue to worry. PostgreSQL isn't MySQL (or a
> typical server application). It reads all database pages into its shared
> memory area. It is wasteful for the DBMS and the OS to both cache this
> data. You'll want the PostgreSQL shared memory size to be around 75% the
> size of RAM (on a dedicated DBMS server). In fact, many commercial DBMS
> systems will use raw writes to bypass the OS cache!
I was concerned about the disk cache because of this link
PostgreSQL counts a lot on the OS to cache data files and
hence does not bother with duplicating its file caching effort.
The shared buffers parameter assumes that OS is going to cache
a lot of files and hence it is generally very low compared
with system RAM. Even for a dataset in excess of 20GB, a
setting of 128MB may be too much, if you have only 1GB RAM
and an aggressive-at-caching OS like Linux.
But now that I have looked a bit more I see that this link
Ideally, the POSTGRESQL shared buffer cache will be:
* Large enough to hold most commonly-accessed tables
* Small enough to avoid swap pagein activity
So I have conflicting documentation.
I have machine with 4Gig of ram. What is the maximum
value of SHMMAX on FreeBSD?
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