Message-ID: <4FDF7456.9010709@enterprisedb.com>
Date: Mon, 18 Jun 2012 21:32:54 +0300
From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
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To: Andres Freund <andres@2ndquadrant.com>
CC: pgsql-hackers@postgresql.org, Robert Haas <robertmhaas@gmail.com>
Subject: Re: WAL format changes
References: <4FDA5136.6080206@enterprisedb.com>
	<CA+TgmobG9VWWvLXeK0XOxoWXtza8JTFgSu2eoAtVFucxH6gLBw@mail.gmail.com>
	<4FDF6E8E.4080900@enterprisedb.com>
	<201206182013.12868.andres@2ndquadrant.com>
In-Reply-To: <201206182013.12868.andres@2ndquadrant.com>
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On 18.06.2012 21:13, Andres Freund wrote:
> On Monday, June 18, 2012 08:08:14 PM Heikki Linnakangas wrote:
>> The page header contains an XLogRecPtr (LSN), so if we change it we'll
>> have to deal with pg_upgrade. I guess we could still keep XLogRecPtr
>> around as the on-disk representation, and convert between the 64-bit
>> integer and XLogRecPtr in PageGetLSN/PageSetLSN. I can try that out -
>> many xlog calculations would admittedly be simpler if it was an uint64.
> I am out of my depth here, not having read any of the relevant code, but
> couldn't we simply replace the lsn from disk with InvalidXLogRecPtr without
> marking the page dirty?
>
> There is the valid argument that you would loose some information when pages
> with hint bits are written out again, but on the other hand you would also
> gain the information that it was a hint-bit write...

Sorry, I don't understand that. Where would you "replace the LSN from 
disk with InvalidXLogRecPtr" ? (and no, it probably won't work ;-) )

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com