Yes, I agree it's unnecessary -- but you'll never have to worry about the 
postmaster not starting due to lack of allocatable
memory -- when I was testing setups, I got sick of rebooting everytime I had to 
make a change to /etc/system, that I threw up my
hands and said, "let it take all it wants".  :)

"single user read only" -- the key is how many connections -- what's your 
application?  Is this being driven by a front end application?

In my case, we run a website with an apache fronted, a tomcat server as 
middleware, and 4 applications.  We may, at times, have only 1
user on, but the java code could be doing a half dozen queries in different 
threads for that one user.

run /usr/ucb/ps -auxww | grep <postgres user name>  (-- we use postgres so "grep 
post" works for us) while under load and see
how many backends are running.  if it's more than 4 or 5, then you are using 
the cpu's.

On the topic of shared memory, watch for the ouput of top or prstat -a -- these 
programs count the shared memory block towards each process
and therefor lie about amount of memory used.  Looking at vmstat, etc show that 
the percentage of utilization reported by top or prstat is
way off, and if you care to examine the memory for each proces, you'll see that 
the shared memory block address is, well, shared by each
process (by definition, eh?) but it can be reported as if it were a different 
block for each process.

Not sure the e3500 is the best box for a data warehouse application

Paul Johnson wrote:

Hi Tom, I've made changes to postgresql.conf as recommended on Josh's site
and this seems to be working well so far.

Given your comments on shared memory, it would appear that the following
entry in /etc/system is unnecessary:

set shmsys:shminfo_shmmax=0xFFFFFFFF

Ironically, we both have this identical setting!

Given that most of our queries are single-user read-only, how do we take
advantage of the 6 CPUs? I'm guessing we can't!?!?!

Also, does this type of workload benefit from moving the txlog?

I'll check our settings against yours given the Solaris 9/E3500 setup that
we both run.

Many thanks,


Hi, Paul

Josh helped my company with this issue -- PG doesn't use shared memory
like Oracle, it depends more on the OS buffers.  Making shared mem
too large a fraction is disasterous and seriously impact performance.
(though I find myself having to justify this to Oracle trained
DBA's) :)

What I found was the biggest performance improvement on the write side was
to turn of file system journaling, and on the read side was
to feed postgres as many CPU's as you can.  What we found for a high use
db (for example backending a web site) is that 8-400 g cpu's
outperforms 2 or 4 fast cpus.  The fast cpu's spend all of their time
context switching as more connections are made.

Also make sure your txlog is on another spindle -- it might even be worth
taking one out of the stripe to do this.

I am running solaris 9 on an e3500 also (though my disc setup is

Here's what I have things set to -- it's probably a pretty good starting
point for you:

# - Memory -

shared_buffers = 65536          # min 16, at least max_connections*2, 8KB
sort_mem = 12000                # min 64, size in KB
vacuum_mem = 64000              # min 1024, size in KB

# - Free Space Map -

max_fsm_pages = 100000          # min max_fsm_relations*16, 6 bytes each
#max_fsm_relations = 10000      # min 100, ~50 bytes each

# - Kernel Resource Usage -

#max_files_per_process = 1000   # min 25
#preload_libraries = ''


and the tail end of /etc/system:

* shared memory config for postgres
set shmsys:shminfo_shmmax=0xFFFFFFFF
set shmsys:shminfo_shmmin=1
set shmsys:shminfo_shmmni=256
set shmsys:shminfo_shmseg=256
set semsys:seminfo_semmap=256
set semsys:seminfo_semmni=512
set semsys:seminfo_semmsl=1000
set semsys:seminfo_semmns=512
* end of shared memory setting
* Set the hme card to force 100 full duplex and not to autonegotiate
* since hme does not play well with cisco
set hme:hme_adv_autoneg_cap=0
set hme:hme_adv_100fdx_cap=1
set hme:hme_adv_100hdx_cap=0
set hme:hme_adv_10fdx_cap=0
set hme:hme_adv_10hdx_cap=0
set hme:hme_adv_100T4_cap=0

Paul Johnson wrote:

Hi Josh, there are 8 internal disks - all are [EMAIL PROTECTED],000 RPM, fibre

The O/S is on 2 mirrored disks, the Postgres cluster is on the /data1
filesystem that is striped across the other 6 disks.

The shared_buffers value is a semi-educated guess based on having made
shared memory available via /etc/system, and having read all we could
on various web sites.

Should I knock it down to 400MB as you suggest?

I'll check out that URL.




I would like to know what /etc/system and postgresql_conf values are

recommended to deliver as much system resource as possible to Postgres. We

use this Sun box solely for single user Postgres data warehousing


What's your disk system?

shared_buffers = 500000

This is highly unlikely to be optimal. That's 3GB. On test linux


up to 8GB, we've not seen useful values of shared buffers anywhere above

400mb. How did you arrive at that figure?

sort_mem = 2097152
vacuum_mem = 1000000

These could be fine on a single-user system. sort_mem is per *sort*


not per query, so you'd need to watch out for complex queries spillling


swap; perhaps set it a 0.5GB or 1GB?
Otherwise, start with the config guide at

Josh Berkus
Aglio Database Solutions
San Francisco

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