From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
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To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
Cc: | pgsql-hackers(at)postgresql(dot)org, Robert Haas <robertmhaas(at)gmail(dot)com> |
Subject: | Re: WAL format changes |
Date: | 2012-06-18 18:32:54 |
Message-ID: | 4FDF7456.9010709@enterprisedb.com |
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Lists: | pgsql-hackers |
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
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