From: "Carlo" <reg01@stonebanks.ca>
To: <pgsql-performance@postgresql.org>
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In-Reply-To: <F545968D-7C4A-41CE-B54D-203F1D4D9FEB@skogoglandskap.no>
Subject: Re: One long transaction or multiple short transactions?
Date: Thu, 8 Oct 2015 11:08:55 -0400
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>> Sounds like a locking problem

This is what I am trying to get at. The reason that I am not addressing
hardware or OS configuration concerns is that this is not my environment,
but my client's. The client is running my import software and has a choice
of how long the transactions can be. They are going for long transactions,
and I am trying to determine whether there is a penalty for single long
transactions over a configuration which would allow for more successive
short transactions. (keep in mind all reads and writes are single-row). 

There are other people working on hardware and OS configuration, and that's
why I can't want to get into a general optimization discussion because the
client is concerned with just this question.

-----Original Message-----
From: Graeme B. Bell [mailto:graeme.bell@nibio.no] 
Sent: October 8, 2015 4:55 AM
To: Carlo
Cc: pgsql-performance@postgresql.org
Subject: Re: [PERFORM] One long transaction or multiple short transactions?

Sounds like a locking problem, but assuming you aren't sherlock holmes and
simply want to get the thing working as soon as possible: 

Stick a fast SSD in there (whether you stay on VM or physical). If you have
enough I/O, you may be able to solve the problem with brute force.
SSDs are a lot cheaper than your time. 

Suggest you forward this to your operators: a talk I have about optimising
multi-threaded work in postgres:  

  http://graemebell.net/foss4gcomo.pdf     (Slides: "Input/Output" in the
middle of the talk and also the slides at the end labelled "For Techies")

Graeme Bell

p.s. You mentioned a VM. Consider making the machine physical and not VM.
You'll get a performance boost and remove the risk of DB corruption from
untrustworthy VM fsyncs. One day there will be a power cut or O/S crash
during these your writes and with a VM you've a reasonable chance of nuking
your DB because VM virtualised storage often doesn't honour fsync (for
performance reasons), but it's fundamental to correct operation of PG. 


> On 08 Oct 2015, at 01:40, Carlo <reg01@stonebanks.ca> wrote:
> 
> 
> I am told 32 cores on a LINUX VM. The operators have tried limiting the
number of threads. They feel that the number of connections is optimal.
However, under the same conditions they noticed a sizable boost in
performance if the same import was split into two successive imports which
had shorter transactions.
>  


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