Message-ID: <4FDF6E8E.4080900@enterprisedb.com>
Date: Mon, 18 Jun 2012 21:08:14 +0300
From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
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To: Robert Haas <robertmhaas@gmail.com>
CC: Andres Freund <andres@2ndquadrant.com>, pgsql-hackers@postgresql.org
Subject: Re: WAL format changes
References: <4FDA5136.6080206@enterprisedb.com>
	<201206142358.12431.andres@2ndquadrant.com>
	<CA+TgmobG9VWWvLXeK0XOxoWXtza8JTFgSu2eoAtVFucxH6gLBw@mail.gmail.com>
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On 18.06.2012 21:00, Robert Haas wrote:
> On Thu, Jun 14, 2012 at 5:58 PM, Andres Freund<andres@2ndquadrant.com>  wrote:
>>> 1. Use a 64-bit segment number, instead of the log/seg combination. And
>>> don't waste the last segment on each logical 4 GB log file. The concept
>>> of a "logical log file" is now completely gone. XLogRecPtr is unchanged,
>>> but it should now be understood as a plain 64-bit value, just split into
>>> two 32-bit integers for historical reasons. On disk, this means that
>>> there will be log files ending in FF, those were skipped before.
>> Whats the reason for keeping that awkward split now? There aren't that many
>> users of xlogid/xcrecoff and many of those would be better served by using
>> helper macros.
>
> I wondered that, too.  There may be a good reason for keeping it split
> up that way, but we at least oughta think about it a bit.

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.

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