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Re: High load average in 64-core server , no I/O wait and CPU is idle

From: "Rajesh Kumar(dot) Mallah" <mallah(at)tradeindia(dot)com>
To: Claudio Freire <klaussfreire(at)gmail(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: High load average in 64-core server , no I/O wait and CPU is idle
Date: 2012-05-24 05:26:47
Message-ID: 32382476.226771337837207313.JavaMail.root@zmbox01.trade-india-local.com (view raw or flat)
Thread:
Lists: pgsql-performance
----- "Claudio Freire" <klaussfreire(at)gmail(dot)com> wrote:

| From: "Claudio Freire" <klaussfreire(at)gmail(dot)com>
| To: "Rajesh Kumar. Mallah" <mallah(at)tradeindia(dot)com>
| Cc: pgsql-performance(at)postgresql(dot)org
| Sent: Thursday, May 24, 2012 9:23:43 AM
| Subject: Re: [PERFORM] High load average in 64-core server , no I/O wait and CPU is idle
|
| On Thu, May 24, 2012 at 12:39 AM, Rajesh Kumar. Mallah
| <mallah(at)tradeindia(dot)com> wrote:
| > The problem is that  sometimes there are spikes of load avg which
| > jumps to > 50 very rapidly ( ie from 0.5 to 50  within 10 secs) and
| > it remains there for sometime and slowly reduces to normal value.
| >
| > During such times of high load average we observe that there is no
| IO wait
| > in system and even CPU is 50% idle. In any case the IO Wait always
| remains < 1.0 % and
| > is mostly 0. Hence the load is not due to high I/O wait which was
| generally
| > the case with our previous hardware.
| 
| Do you experience decreased query performance?


Yes we do experience substantial application performance degradations.


| 
| Load can easily get to 64 (1 per core) without reaching its capacity.
| So, unless you're experiencing decreased performance I wouldn't think
| much of it.

I far as i understand ,
Load Avg is the average number of processes waiting to be run in past 1 , 
5 or 15 mins. A number > 1 would mean that countable number of processes
were waiting to be run. how can load of more than 1 and upto 64 be OK
for a 64 core machine ?



| 
| Do you have mcelog running? as a cron or a daemon?


No we do not have mcelog.

BTW the Postgresql version is : 9.1.3 which i forgot to mention 
in my last email.


regds
mallah.

| Sometimes, mcelog tends to crash in that way. We had to disable it in
| our servers because it misbehaved like that. It only makes load avg
| meaningless, no performance impact, but being unable to accurately
| measure load is bad enough.

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Next:From: Claudio FreireDate: 2012-05-24 05:44:32
Subject: Re: High load average in 64-core server , no I/O wait and CPU is idle
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Subject: Re: Configuration Recommendations

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