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Re: SSD performance

From: Jeff <threshar(at)torgo(dot)978(dot)org>
To: Scott Carey <scott(at)richrelevance(dot)com>
Cc: "david(at)lang(dot)hm" <david(at)lang(dot)hm>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: SSD performance
Date: 2009-02-03 17:54:53
Message-ID: 742C5996-F5CE-4F2C-803C-CFA747F36ACC@torgo.978.org (view raw or flat)
Thread:
Lists: pgsql-performance
I somehow managed to convince the powers that be to let me get a  
couple X25-E's.
I tossed them in my macpro (8 cores), fired up Ubuntu 8.10 and did  
some testing.

Raw numbers are very impressive. I was able to get 3700 random seek 
+read's a second. In a R1 config it stayed at 3700, but if I added  
another process it went up to 7000, and eventually settled into the  
4000s.    If I added in some random writing with fsyncs to it, it  
settled at 2200 (to be specific, I had 3 instances going - 2 read-only  
and 1 read-20% write to get that).  These numbers were obtained  
running a slightly modified version of pgiosim (which is on  
pgfoundtry) - it randomly seeks to a "block" in a file and reads 8kB  
of data, optionally writing the block back out.

Now, moving into reality I compiled 8.3.latest and gave it a whirl.   
Running against a software R1 of the 2 x25-e's  I got the following  
pgbench results:
(note config tweaks: work_mem=>4mb, shared_buffers=>1gb, should  
probably have tweaked checkpoint_segs, as it was emitting lots of  
notices about that, but I didn't).

(multiple runs, avg tps)

Scalefactor 50, 10 clients: 1700tps

At that point I realized write caching on the drives was ON. So I  
turned it off at this point:

Scalefactor 50, 10 clients: 900tps

At scalefactor 50 the dataset fits well within memory, so I scaled it  
up.

Scalefactor 1500: 10 clients: 420tps


While some of us have arrays that can smash those numbers, that is  
crazy impressive for a plain old mirror pair.   I also did not do much  
tweaking of PG itself.

While I'm in the testing mood, are there some other tests folks would  
like me to try out?

--
Jeff Trout <jeff(at)jefftrout(dot)com>
http://www.stuarthamm.net/
http://www.dellsmartexitin.com/




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