From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andreas Pflug <pgadmin@pse-consulting.de>
Cc: Bob Ippolito <bob@redivi.com>
Cc: Mark Cotner <mcotner@yahoo.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: sustained update load of 1-2k/sec
Date: Fri, 19 Aug 2005 10:09:05 -0400
Message-ID: <18000.1124460545@sss.pgh.pa.us> (raw)
In-Reply-To: <4305E57E.1010604@pse-consulting.de>
References: <20050819082404.53751.qmail@web32915.mail.mud.yahoo.com>
<67788A4A-4011-49AB-B329-683FD9532661@redivi.com>
<17690.1124458553@sss.pgh.pa.us>
<4305E57E.1010604@pse-consulting.de>
Andreas Pflug <pgadmin@pse-consulting.de> writes:
> Tom Lane wrote:
>> As far as the question "can PG do 1-2k xact/sec", the answer is "yes
>> if you throw enough hardware at it". Spending enough money on the
>> disk subsystem is the key ...
>>
> The 1-2k xact/sec for MySQL seems suspicious, sounds very much like
> write-back cached, not write-through, esp. considering that heavy
> concurrent write access isn't said to be MySQLs strength...
> I wonder if preserving the database after a fatal crash is really
> necessary, since the data stored sounds quite volatile; in this case,
> fsync=false might be sufficient.
Yeah, that's something to think about. If you do need full transaction
safety, then you *must* have a decent battery-backed-write-cache setup,
else your transaction commit rate will be limited by disk rotation
speed --- for instance, a single connection can commit at most 250 xacts
per second if the WAL log is on a 15000RPM drive. (You can improve this
to the extent that you can spread activity across multiple connections,
but I'm not sure you can expect to reliably have 8 or more connections
ready to commit each time the disk goes 'round.)
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, pgadmin@pse-consulting.de, bob@redivi.com, mcotner@yahoo.com
Subject: Re: sustained update load of 1-2k/sec
In-Reply-To: <18000.1124460545@sss.pgh.pa.us>
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