Message-ID: <49DF7EB8.8070009@agliodbs.com>
Date: Fri, 10 Apr 2009 10:15:36 -0700
From: Josh Berkus <josh@agliodbs.com>
Organization: PostgreSQL Experts Inc.
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To: "Joshua D. Drake" <jd@commandprompt.com>
CC: pgsql-performance@postgresql.org
Subject: Re: Using IOZone to simulate DB access patterns
References: <49D697F7.2040304@agliodbs.com> <49D6A551.5080001@agliodbs.com>
	<1239379233.19518.361.camel@jd-laptop.pragmaticzealot.org>
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JD,

> In order to test real interactivity (AFAIK) with iozone you have to
> launch multiple iozone instances. You also need to do them from separate
> directories, otherwise it all starts writing the same file. The work I
> did here:

Actually, current IOZone allows you to specify multiple files.   For 
example, the command line I was using:

iozone -R -i 0 -i 1 -i 2 -i 3 -i 4 -i 5 -i 8 -l 6 -u 6 -r 8k -s 4G -F f1 
f2 f3 f4 f5 f6

And it does indeed launch 6 processes under that configuration. 
However, I found that for pretty much all of the write tests except for 
the first the processes blocked each other:


F S   UID   PID  PPID  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
0 S    26  6061  5825  0  80   0 - 11714 wait   pts/3    00:00:00 iozone
1 D    26  6238  6061  0  78   0 - 11714 sync_p pts/3    00:00:03 iozone
1 D    26  6239  6061  0  78   0 - 11714 sync_p pts/3    00:00:03 iozone
1 D    26  6240  6061  0  78   0 - 11714 sync_p pts/3    00:00:03 iozone
1 D    26  6241  6061  0  78   0 - 11714 sync_p pts/3    00:00:03 iozone
1 D    26  6242  6061  0  78   0 - 11714 stext  pts/3    00:00:03 iozone
1 R    26  6243  6061  0  78   0 - 11714 -      pts/3    00:00:03 iozone


Don Capps says that the IOZone code is perfect, and that pattern 
indicates a problem with my system, which is possible.  Can someone else 
try concurrent IOZone on their system and see if they get the same 
pattern?  I just don't have that many multi-core machines to test on.

Also, WTF is the difference between "Children See" and "Parent Sees"? 
IOZone doesn't document this anywhere.

-- 
Josh Berkus
PostgreSQL Experts Inc.
www.pgexperts.com