From: Andres Freund <andres@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: PostgreSQL Bugs <pgsql-bugs@postgresql.org>
Subject: Re: pg_upgrade < 9.3 -> >=9.3 misses a step around multixacts
Date: Mon, 21 Jul 2014 01:12:14 +0200
Message-ID: <20140720231214.GH5974@alap3.anarazel.de> (raw)
In-Reply-To: <18673.1405897470@sss.pgh.pa.us>
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<20140720213258.GD5974@alap3.anarazel.de>
<16274.1405892584@sss.pgh.pa.us>
<20140720220253.GE5974@alap3.anarazel.de>
<17255.1405894611@sss.pgh.pa.us>
<20140720223010.GF5974@alap3.anarazel.de>
<17935.1405895946@sss.pgh.pa.us>
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On 2014-07-20 19:04:30 -0400, Tom Lane wrote:
> Andres Freund <andres@2ndquadrant.com> writes:
> > If any *single* full table vacuum after that calls
> > vac_update_datfrozenxid() which just needs its datfrozenxid advance by
> > one we're in trouble: vac_truncate_clog() will be called with minMulti =
> > GetOldestMultiXactId().
>
> Uh, no, the cutoff is GetOldestMultiXactId minus
> vacuum_multixact_freeze_min_age (or the autovac equivalent).
> See vacuum_set_xid_limits.
Unfortunately not :(. The stuff computed in vacuum_set_xid_limits isn't
used for truncation - which normally is sane because another database
might be further behind.
void
vac_update_datfrozenxid(void)
{
...
MultiXactId newMinMulti;
...
/*
* Similarly, initialize the MultiXact "min" with the value that would be
* used on pg_class for new tables. See AddNewRelationTuple().
*/
newMinMulti = GetOldestMultiXactId();
...
while ((classTup = systable_getnext(scan)) != NULL)
{
...
if (MultiXactIdPrecedes(classForm->relminmxid, newMinMulti))
newMinMulti = classForm->relminmxid;
}
...
if (dirty || ForceTransactionIdLimitUpdate())
vac_truncate_clog(newFrozenXid, newMinMulti);
}
But even if it were, I don't really see how that changes anything?
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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To: pgsql-bugs@postgresql.org
Cc: andres@2ndquadrant.com, tgl@sss.pgh.pa.us, bruce@momjian.us, alvherre@2ndquadrant.com
Subject: Re: pg_upgrade < 9.3 -> >=9.3 misses a step around multixacts
In-Reply-To: <20140720231214.GH5974@alap3.anarazel.de>
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