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Re: COMMIT NOWAIT Performance Option

From: Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>
To: Gregory Stark <stark(at)enterprisedb(dot)com>
Cc: "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com>, pgsql-hackers(at)postgresql(dot)org, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>
Subject: Re: COMMIT NOWAIT Performance Option
Date: 2007-02-28 15:57:03
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Gregory Stark wrote:
> "Jonah H. Harris" <jonah(dot)harris(at)gmail(dot)com> writes:
>> This proposed design is overcomplicated and a waste of space.  I mean,
>> we reduce storage overhead using phantom command id and variable
>> varlena, but let's just fill it up again with unnecessary junk bytes.
> We reduced storage overhead using phantom command id by 8 bytes *per tuple*. I
> hardly think 8 bytes per page is much of a concern. You're already losing an
> average of 1/2 a tuple per page to rounding and that's a minimum of 16 bytes
> for the narrowest of tuples.
>>> That seems pretty unlikely. CRC checks are expensive cpu-wise, we're already
>>> suffering a copy due to our use of read/write the difference between
>>> read/write of 8192 bytes and readv/writev of 511b*16+1*6 is going to be
>>> non-zero but very small. Thousands of times quicker than the CRC.
>> Prove it.
> We've already seen wal CRC checking show up at the top of profiles.

yeah - on fast boxes (diskio wise) wal-crc checking is nearly always on 
the very top of wal-intensive workloads.


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