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Re: Low CPU Usage

From: brauagustin-susc(at)yahoo(dot)com(dot)ar
To: Jean-David Beyer <jeandavid8(at)verizon(dot)net>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Low CPU Usage
Date: 2007-09-20 17:28:37
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Lists: pgsql-performance
My new server postgresql.conf is equal to the old one. I'm doubting this is a hardware issue.
Googling with my hard HP Proliant ML 110 G3 I saw that IHC7 controller has some problems, but looking and testing with hdparm it looks ok.
hdparm -tT /dev/sdaç
Timing cached reads: 1722 MB in 2.00 seconds = 860.38 MB/sec
Timing buffered disks reads: 164 MB in 3.01 seconds = 54.53 MB/sec

Doing hdparm -I /dev/sda
DMA has * in udma5
Which other test can I do to find if this is a hardware, kernel o postgres issue?


----- Mensaje original ----
De: Jean-David Beyer <jeandavid8(at)verizon(dot)net>
Para: pgsql-performance(at)postgresql(dot)org
Enviado: jueves 20 de septiembre de 2007, 9:31:36
Asunto: Re: [PERFORM] Low CPU Usage

brauagustin-susc(at)yahoo(dot)com(dot)ar wrote:
> Hola Beto.
> I have no idea where to look for that configuration or settings.

In postgreSQL, the main settings are in .../pgsql/data/postgresql.conf

> Yesterday I red about some drivers problems with SATA disk working
> togheter with IDE devices with DMA.
> Mi server server is a Pentium VI 3.3 with hyper threading (enabled in
> BIOS), HP Proliant ML 110.
> Then I entered to the BIOS and saw in IDE Configuration:
>   ATA/IDE Configuration                    [Enhanced]
>           Configure SATA as                   [IDE]  => it has RAID
> option too
> I have any idea how to continue!!! I don't know if this a SATA problem,
> a configuration problem or what else. I have installed several servers
> beggining with postgres 6.4 and I've neved had this kind of problems
> (always with IDE disks). I think this is a problem with SATA disk i/o,
> but I don't see how to measure that (I have already set postgresql.conf).

Are you sure you are really having a problem with insufficient CPU time
being devoted to your program(s)? When I run postgreSQL and do the initial
populating of my database, which takes several hours due to the nature of
the input data, it runs just 25% to 50% of one CPU, even though I have two
3.06 GHz hyperthreaded Xeon processors and six 10,000 rpm Ultra/320 SCSI
hard drives on two SCSI controllers. If I look at the results of the Linux
top command, and iostat and vmstat, I see that I am in io-wait state 100% of
the time. The transfer rate to the hard drives averages about 2
Megabytes/second even though I have seen 90 Megabytes/second at times (when
doing a database restore). So the IO system can be quite fast when it is not
waiting (for seeks, no doubt). If the postgreSQL processes wanted more CPU
time, they could have it as the machine does not do much else most of the
time. Actually, it runs a four BOINC processes, but they run at nice level
19, so they run only if no other process wants processing time. When I do a
database backup, it will run more than 100% of a CPU (remember I have two or
four processors, depending on how you count them) for extended periods, so
the OS is certainly capable of supplying CPU power when I need it. And
postgreSQL runs multiple processes at once, so in theory, they could gert
400% of a processor if they needed it. They do not seem to need to do this
for me.
> Regards
> Agustin
> ----- Mensaje original ----
> De: Norberto Meijome <beto(at)octantis(dot)com(dot)au>
> Para: brauagustin-susc(at)yahoo(dot)com(dot)ar
> CC: pgsql-performance(at)postgresql(dot)org
> Enviado: jueves 20 de septiembre de 2007, 7:53:05
> Asunto: Re: [PERFORM] Low CPU Usage
> On Wed, 19 Sep 2007 12:13:33 -0700 (PDT)
> brauagustin-susc(at)yahoo(dot)com(dot)ar wrote:
>> max_stack_depth = 7MB #in the old server is 8MB but if I set in here
> give me the ulimit error
> Hola Agustin :)
> otro argentino en el extranjero x aca ;)
> anyway, back to English ;)
> a long shot but...
> check if you have any limits set on the host for CPU usage... you may be
> limited to x number of secs / % by the OS scheduler. When you query your
> CPU,
> it will say u are only using 5% or so...

  .~.  Jean-David Beyer          Registered Linux User 85642.
  /V\  PGP-Key: 9A2FC99A         Registered Machine   241939.
 /( )\ Shrewsbury, New Jersey
 ^^-^^ 08:15:01 up 6 days, 42 min, 1 user, load average: 4.24, 4.25, 4.14

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