From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
---|---|
To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Hot Standby dev build (v8) |
Date: | 2009-01-16 20:09:35 |
Message-ID: | 4970E97F.9040504@enterprisedb.com |
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Lists: | pgsql-hackers |
Simon Riggs wrote:
> On Fri, 2009-01-16 at 16:33 +0200, Heikki Linnakangas wrote:
>> I don't think RecentGlobalXmin is good enough here:
>>
>>> ! /*
>>> ! * We would like to set an accurate latestRemovedXid, but there
>>> ! * is no easy way of obtaining a useful value. So we use the
>>> ! * probably far too conservative value of RecentGlobalXmin instead.
>>> ! */
>>> ! xlrec_delete.latestRemovedXid = RecentGlobalXmin;
>>> ! rdata[0].data = (char *) &xlrec_delete;
>>> ! rdata[0].len = SizeOfBtreeDelete;
>> RecentGlobalXmin is just a hint, it lags behind the real oldest xmin
>> that GetOldestXmin() would return. If another backend has a more recent
>> RecentGlobalXmin value, and has killed more recent tuples on the page,
>> the latestRemovedXid written here is too old.
>
> What do you think we should do instead?
Dunno. Maybe call GetOldestXmin().
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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