Tuning for PostGreSQL Database

[Tom Samplonius]

On Sat, 19 Jul 2003, Paul Pathiakis wrote:

> Hi,
> 
> 	I'm trying to setup a dedicated PostGreSQL Database server.  First off, don't 
> get me going on the inadequacies of the hardware setup,  I am a sysadmin with 
> a partial clue.  :-) (The hardware was bought without any input from me for 
> demo purposes.)  It's an Intel board with twin 2.8 GHZ processors and Promise 
> ATA Fastrack RAID built-in, 1 GB of RAM.   Since this is just a 
> throughput/response test against SuSe Linux Enterprise Server, Windows XP and 
> FreeBSD, I'm going to break the mirror and try to do some intelligence about 
> at least trying to log to a different drive.  Anyhow, there are 2-3 drives in 
> this box, no scsi, nothing.  I want it to perform like no tomorrow on 

  You don't really mention the nature of the test that you will running.
Read intensive?  Write intensive?  25/75 mix?  Number of clients?

> 	FreeBSD 4.8 or 5.1?

  Probably 5.1-RELEASE.

> 	OS configuration, any suggestions on SWAP layout, how much swap,
> both drives?

  As always, swap should be twice that of RAM.  Ideally, depending on what
the test consists of, you won't use swap at all.

> 	Are there optimal parameters for sizing on the disk throughput?  
> That is, newfs parameters, i-node configuration, tunefs parameters,
> async on the drives, etc?  (consider nothing trivial, please feel free
> to just lay into this like I'm a newbie - considering my
> not-so-extensive experience with PostgreSQL)

  Well, it is database app, so very little on the filesystem is going to
help.  PostgreSQL will create a bunch of bunch of files, and randomly read
and write into them.  

> 	Should I keep softupdates on or off?  This is a db and I am
> constrained by data integrity issues, however, I'm looking for as much
> speed as possible given the limited setup.

  Softupdates on, async off.  Softupdates is just a better async.
However, neither is going to help or hurt you much anyhow.  Both
softupdates and sync change how meta data is written to disk.  Once the
database files are created, meta data isn't much of any issue.

> 	what is the best layout of OS, PostgreSQL, and PostgreSQL
> logging on a 2 disk configuration?  3 disk configuration?

  Well, the database and the logs should be on separate devices.  If the
database can be broken up, do that too.  I don't know that the OS files
will be accessed much after boot, so that really isn't going to cause any
significant load.

> 	Is there anything that I should put in the following files for
> tuning:
> 
> 	systrcl.conf  (semaphore and shared memory configurations, etc?)

  Well, you need to increase the semaphores and shared memory
configuration limits to match whatever you plan to give to PostgreSQL.  I
don't know whether the test consists of.  If the test database is large,
you'll want a large shared memory area.  But I find that many people do
tests with tiny non-real-world databases.  It is pointless to make the
shared area larger than the database size!  Plus, you need some memory
available for client connections.  Don't know how many clients you will
have connecting.

> 	loader.conf (hw.ata.atapi_dma on or off?  how do I make the
...

  DMA should probably be on, as long as your disks can handle it.

  You will have to test with HyperThreading too.  If the client count is
large, HyperThreading might help.  However, it might increase latency.  
No idea if you test measures latency!  If the test is just raw throughput
with lots of clients, HTT is probably going to help.  However, if you
never have more than 4 connected clients, probably not.

> 	If there's additional reading, let me know.  I'm more than happy
> to follow links, read more about PostgreSQL, etc.
> 
> 	Thank you all!
> 
> 	Paul Pathiakis


Tom