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Re: [HACKERS] Full page writes improvement, code update

From: Koichi Suzuki <suzuki(dot)koichi(at)oss(dot)ntt(dot)co(dot)jp>
To: Zeugswetter Andreas ADI SD <ZeugswetterA(at)spardat(dot)at>
Cc: Hannu Krosing <hannu(at)skype(dot)net>, "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Simon Riggs <simon(at)2ndquadrant(dot)com>, josh(at)agliodbs(dot)com, pgsql-hackers(at)postgresql(dot)org, pgsql-patches(at)postgresql(dot)org
Subject: Re: [HACKERS] Full page writes improvement, code update
Date: 2007-04-26 01:19:45
Message-ID: 462FFE31.6050707@oss.ntt.co.jp (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
Hi,

Zeugswetter Andreas ADI SD wrote:
>> I don't insist the name and the default of the GUC parameter. 
>>  I'm afraid wal_fullpage_optimization = on (default) makes 
>> some confusion because the default behavior becomes a bit 
>> different on WAL itself.
> 
> Seems my wal_fullpage_optimization is not a good name if it caused
> misinterpretation already :-(
> 
>>>> Amount of WAL after 60min. run of DBT-2 benchmark 
>>>> wal_add_optimization_info = off (default) 3.13GB
>>> how about wal_fullpage_optimization = on (default)
> 
> The meaning of wal_fullpage_optimization = on (default)
> would be the same as your wal_add_optimization_info = off (default).
> (Reversed name, reversed meaning of the boolean value)
> 
> It would be there to *turn off* the (default) WAL full_page
> optimization.
> For your pg_compresslog it would need to be set to off. 
> "add_optimization_info" sounded like added info about/for some
> optimization
> which it is not. We turn off an optimization with the flag for the
> benefit
> of an easier pg_compresslog implementation.

For pg_compresslog to remove full page writes, we need 
wal_add_optimization_info=on.

> 
> As already said I would decouple this setting from the part that sets
> the "removeable full page" flag in WAL, and making the recovery able to
> skip dummy records. This I would do unconditionally.
> 
> Andreas
> 
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-- 
-------------
Koichi Suzuki

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