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Re: "Priority Mechanisms for OLTP and Transactional Web Applications"

From:	"Dann Corbit" <DCorbit(at)connx(dot)com>
To:	<cache+(at)cs(dot)cmu(dot)edu>
Cc:	<harchol(at)cs(dot)cmu(dot)edu>, <natassa(at)cmu(dot)edu>, <bianca(at)cs(dot)cmu(dot)edu>, <cache(at)cs(dot)cmu(dot)edu>, "PostgreSQL-development" <pgsql-hackers(at)postgresql(dot)org>
Subject:	Re: "Priority Mechanisms for OLTP and Transactional Web Applications"
Date:	2005-05-04 18:43:02
Message-ID:	D425483C2C5C9F49B5B7A41F89441547055B49@postal.corporate.connx.com
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Yes. Something simple that can provide clear, tangible benefits is the
best kind of improvement.

I am sure that adding parameters to the command line of PostgreSQL which
enables superior tuning for differing computer systems would be wildly
appreciated.

> -----Original Message-----
> From: cache+(at)cs(dot)cmu(dot)edu [mailto:cache+(at)cs(dot)cmu(dot)edu]
> Sent: Wednesday, May 04, 2005 11:40 AM
> To: Dann Corbit
> Cc: harchol(at)cs(dot)cmu(dot)edu; natassa(at)cmu(dot)edu; bianca(at)cs(dot)cmu(dot)edu;
> cache(at)cs(dot)cmu(dot)edu
> Subject: "Priority Mechanisms for OLTP and Transactional Web
Applications"
>
>
> In our experimentation, we simply used a user-defined function to
> handle changing the priority of transactions' threads. It shouldn't
> be hard to port the implementation back into postgres --- and
> provide an administrative mechanism to assign priorities. Do you
> think that PostgreSQL core would be interested in integrating
> priorities of service in this manner? I'd be very interested in
> helping out with this.
>
> -David
>
>
> Dann Corbit writes:
> > I have a question about your conclusion and the experiments as they
> > relate to the PostgreSQL database. In the paper, we find this:
> >
> >
> >
> > "For example, we find that for PostgreSQL running under TPC-C, the
> > simplest CPU scheduling algorithm CPU-Prio provides a factor of 2
> > improvement for the high-priority transactions, and adding priority
> > inheritance (CPU-Prio-Inherit) brings this up to a factor of near 6
> > improvement under high loads, while hardly penalizing low-priority
> > transactions. For PostgreSQL running under the TPC-W workload, we
find
> > that the best scheduling algorithm is the simplest CPU scheduling
> policy
> > CPU-Prio, which improves performance for high-priority transactions
by
> a
> > factor of up to 5. The reason why inheritance is more effective for
the
> > TPC-C example above is that TPC-C has much more data contention
than
> > TPC-W, leading to more priority inversions."
> >
> >
> >
> > To change the scheduling of the threads, did you modify the source
code
> > of the PostgreSQL database? If so, are the modifications
available?
> >
> >
> >
> > It seems that you have achieved a very significant performance
boost by
> > a priority change, and I would be interested to know if the
> > modifications are available and also if they can be plowed back
into
> the
> > PostgreSQL core.
> >
> >
> >
> > <html xmlns:o="urn:schemas-microsoft-com:office:office"
> xmlns:w="urn:schemas-microsoft-com:office:word"
> xmlns="http://www.w3.org/TR/REC-html40">
> >
> > <head>
> > <META HTTP-EQUIV="Content-Type" CONTENT="text/html;
charset=us-ascii">
> > <meta name=Generator content="Microsoft Word 11 (filtered medium)">
> > <style>
> > 
> > </style>
> >
> > </head>
> >
> > <body lang=EN-US link=blue vlink=purple>
> >
> > <div class=Section1>
> >
> > size:10.0pt;
> > font-family:Arial'>I have a question about your conclusion and the
> experiments
> > as they relate to the PostgreSQL database.  In the paper, we
find
> this:<o:p></o:p>
> >
> > size:10.0pt;
> > font-family:Arial'><o:p> </o:p>
> >
> > size:10.0pt;
> > font-family:Arial'>"For example, we find that for PostgreSQL
> running under
> > TPC-C, the simplest CPU scheduling algorithm CPU-Prio provides a
factor
> of 2
> > improvement for the high-priority transactions, and adding priority
> inheritance
> > (CPU-Prio-Inherit) brings this up to a factor of near 6 improvement
> under high
> > loads, while hardly penalizing low-priority transactions.  For
> PostgreSQL
> > running under the TPC-W workload, we find that the best scheduling
> algorithm is
> > the simplest CPU scheduling policy CPU-Prio, which improves
performance
> for
> > high-priority transactions by a factor of up to 5. The reason why
> inheritance
> > is more effective for the TPC-C example above is that TPC-C has
much
> more data
> > contention than TPC-W, leading to more priority
> inversions."<o:p></o:p>
> >
> > size:10.0pt;
> > font-family:Arial'><o:p> </o:p>
> >
> > size:10.0pt;
> > font-family:Arial'>To change the scheduling of the threads, did you
> modify the
> > source code of the PostgreSQL database?  If so, are the
> modifications
> > available?<o:p></o:p>
> >
> > size:10.0pt;
> > font-family:Arial'><o:p> </o:p>
> >
> > size:10.0pt;
> > font-family:Arial'>It seems that you have achieved a very
significant
> > performance boost by a priority change, and I would be interested
to
> know if
> > the modifications are available and also if they can be plowed back
> into the
> > PostgreSQL core.<o:p></o:p>
> >
> > size:10.0pt;
> > font-family:Arial'><o:p> </o:p>
> >
> > </div>
> >
> > </body>
> >
> > </html>
>
> --
> Hollywood is where if you don't have happiness you send out for it.
> -- Rex Reed

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