From: Mark Kirkwood <markir@paradise.net.nz>
To: Ron Mayer <rm_pg@cheapcomplexdevices.com>
Cc: Andreas Kostyrka <andreas@kostyrka.org>
Cc: jim@nasby.net
Cc: pgsql-performance@postgresql.org
Subject: Re: RES: Priority to a mission critical transaction
Date: Wed, 29 Nov 2006 14:27:54 +1300
Message-ID: <456CE21A.4010004@paradise.net.nz> (raw)
In-Reply-To: <456C9CA0.3040604@cheapcomplexdevices.com>
References: <20061127005143.GJ39519@nasby.net>
<PEEPKDFEHHEMKBBFPOOKMEAIDKAA.carlos.reimer@opendb.com.br>
<20061128192036.GB7489@andi-lap.la.revver.com>
<456C9CA0.3040604@cheapcomplexdevices.com>
Ron Mayer wrote:
> Short summary:
> * Papers studying priority inversion issues with
> databases including PosgreSQL and realistic workloads
> conclude setpriority() helps even in the presence of
> priority inversion issues for TCP-C and TCP-W like
> workloads.
> * Avoiding priority inversion with priority inheritance
> will further help some workloads (TCP-C) more than
> others (TCP-W) but even without such schedulers
> priority inversion does not cause as much harm
> as the benefit you get from indirectly scheduling
> I/O through setpriority() in any paper I've seen.
>
> Andreas Kostyrka wrote:
>> * Carlos H. Reimer <carlos.reimer@opendb.com.br> [061128 20:02]:
>>> Will the setpriority() system call affect i/o queue too?
>> Nope, and in fact the article shows the way not to do it.
>
> Actually *YES* setpriority() does have an indirect effect
> on the I/O queue.
>
While I was at Greenplum a related point was made to me:
For a TPC-H/BI type workload on a well configured box the IO subsystem
can be fast enough so that CPU is the bottleneck for much of the time -
so being able to use setpriority() as a resource controller makes sense.
Also, with such a workload being mainly SELECT type queries, the dangers
connected with priority inversion are considerably reduced.
Cheers
Mark
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To: pgsql-performance@postgresql.org
Cc: markir@paradise.net.nz, rm_pg@cheapcomplexdevices.com, andreas@kostyrka.org, jim@nasby.net
Subject: Re: RES: Priority to a mission critical transaction
In-Reply-To: <456CE21A.4010004@paradise.net.nz>
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