Re: Basic performance tuning on dedicated server - Mailing list pgsql-performance

On Thu, Mar 10, 2011 at 3:12 AM, runner <runner@winning.com> wrote:
>
> I'm setting up my first PostgreSQL server to replace an existing MySQL
> server.  I've been reading Gregory Smith's book Postgres 9.0 High
> Performance and also Riggs/Krosing's PostgreSQL 9 Administration Cookbook.
> While both of these books are excellent, I am completely new to PostgreSQL
> and I cannot possibly read and understand every aspect of tuning in the
> short amount time before I have to have this server running.
>
> I started out by using the 11 step process for tuning a new dedicated server
> (page 145 in Gregory Smith's book) but I found I had more questions than I
> could get answered in the short amount of time I have.  So, plan B is to use
> pgtune to get a ballpark configuration and then fine tune later as I learn
> more.
>
> I ran some performance tests where I imported my 11Gb database from our old
> MySQL server into PostgreSQL 9.0.3.  In my testing I left the
> postgresql.conf at default values.  The PostgreSQL test database completely
> blew away the old MySQL server in performance.  Again, the postgresql.conf
> was never optimized so I feel I will be OK if I just get in the ballpark
> with tuning the postgresql.conf file.
>
> I'd like to run my plan by you guys to see if it seems sane and make sure
> I'm not leaving out anything major.
>
> I'll be running PostgreSQL 9.0.3 on a Solaris 10 64 bit (Sparc) box with 16G
> of RAM.    The local file system is ZFS.  The database file systems are UFS
> and are SAN mounted from VERY fast disks with battery backed write cache.  I
> don't know anybody else who is running a mix of ZFS and UFS file systems,  I
> cannot change this.  ZFS has it's own file system cache so I'm concerned
> about the ramifications of having caches for both ZFS and UFS. The only
> database related files that are stored on the local ZFS file system are the
> PostgreSQL binaries and the system logs.
>
> From the extensive reading I've done, it seems generally accepted to set the
> UFS file system cache to use 50% of the system RAM.  That leaves 8G left for
> PostgreSQL.  Well, not really 8G,  I've reserved 1G for system use which
> leaves me with 7G for PostgreSQL to use.  I ran pgtune and specified 7G as
> the memory ( 7 * 1024 * 1024 = 7340032 ) and 300 connections.  The resulting
> postgresql.conf is what I plan to use.
>
> After reading Gregory Smith's book, I've decided to put the database on one
> UFS file system, the WAL on a separate UFS file system (mounted with
> forcedirectio) and the archive logs on yet another UFS file system.  I'll be
> on Solaris 10 so I've set wal_sync_method = fdatasync based on
> recommendations from other Solaris users.  Did a lot of google searches on
> wal_sync_method and Solaris.
>
> That's what I plan to go live with in a few days.  Since my test server with
> default configs already blows away the old database server, I think I can
> get away with this strategy.  Time is not on my side.
>
> I originally installed the 32 bit PostgreSQL binaries but later switched to
> 64 bit binaries.  I've read the 32 bit version is faster and uses less
> memory than the 64 bit version.  At this point I'm assuming I need the 64
> bit binaries in order to take full advantage the the 7G of RAM I have
> allocated to PostgreSQL.  If I am wrong here please let me know.
>
> This has been a lot of information to cram down in the short amount of time
> I've had to deal with this project.  I'm going to have to go back and read
> the PostgreSQL 9.0 High Performance book two or three more times and really
> dig in to the details but for now I'm going to cheat and use pgtune as
> described above.  Thank you in advance for any advice or additional tips you
> may be able to provide.


congratulations!

postgres memory tuning is a complicated topic but most it tends to be
very subtle in its effects or will apply to specific situations, like
dealing with i/o storms during checkpooints.  The only settings that
often need to be immediately cranked out of the box are
maintenance_work_mem and (much more carefully) work_mem.

Regardless how shared buffers is set, ALL of your server's memory goes
to postgres less what the o/s keeps for itself and other applications.
 You do not allocate memory to postgres -- you only suggest how it
might be used.   I stopped obsessing how it was set years ago.  In
fact, on linux for example dealing with background dirty page flushing
via the o/s (because stock settings can cause i/o storms) is a bigger
deal than shared_buffers by about an order of magnitude imnsho.

The non memory related settings of postgresql.conf, the planner
settings (join/from collapse limit, random_page_cost, etc), i/o
settings (fsync, wal_sync_method etc) are typically much more
important for performance than how memory is set up.

The reason postgres is showing up mysql is almost certainly due to the
query planner and/or (if you were using myisam) reaping the benefits
of mvcc.  My knowledge of mysql stops at the 5.0/5.1 era, but I can
tell you postgres is a much more sophisticated platform in very many
levels, and you will be happy you made the switch!

merlin