From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: buschmann@nidsa.net
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #16045: vacuum_db crash and illegal memory alloc after pg_upgrade from PG11 to PG12
Date: Mon, 14 Oct 2019 10:16:40 -0400
Message-ID: <27596.1571062600@sss.pgh.pa.us> (raw)
In-Reply-To: <20191013203848.2eksimmpux3546wr@development>
References: <20191009232836.jg77wccqwy5fgs6s@development>
<20265.1570664514@sss.pgh.pa.us>
<20191010014813.3b2btmkakhrskwgd@alap3.anarazel.de>
<20191010134303.bkwjzchjb2w66iro@development>
<30706.1570717152@sss.pgh.pa.us>
<20191010163350.2rtcjtje6tkgilqi@development>
<1542.1570738460@sss.pgh.pa.us>
<20191010204022.6hiiubm2cueu3ghk@development>
<20191013001032.lqrn4kqaovhrf77l@development>
<17717.1570991208@sss.pgh.pa.us>
<20191013203848.2eksimmpux3546wr@development>
Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
> On Sun, Oct 13, 2019 at 02:26:48PM -0400, Tom Lane wrote:
>> Might be a good idea to exclude attisdropped columns in the part of the
>> recursive query that's looking for sql_identifier columns of composite
>> types. I'm not sure if composites can have dropped columns today,
[ I checked this, they can ]
>> but even if they can't it seems like a wise bit of future-proofing.
>> (We'll no doubt have occasion to use this logic again...)
> Hmm? How could that be safe? Let's say we have a composite type with a
> sql_identifier column, it's used in a table with data, and we drop the
> column. We need the pg_type information to parse the existing, so how
> could we skip attisdropped columns?
It works exactly like it does for table rowtypes.
regression=# create type cfoo as (f1 int, f2 int, f3 int);
CREATE TYPE
regression=# alter type cfoo drop attribute f2;
ALTER TYPE
regression=# select attname,atttypid,attisdropped,attlen,attalign from pg_attribute where attrelid = 'cfoo'::regclass;
attname | atttypid | attisdropped | attlen | attalign
------------------------------+----------+--------------+--------+----------
f1 | 23 | f | 4 | i
........pg.dropped.2........ | 0 | t | 4 | i
f3 | 23 | f | 4 | i
(3 rows)
All we need to skip over the dead data is attlen/attalign, which are
preserved in pg_attribute even if the pg_type row is gone.
As this example shows, you don't really *have* to check attisdropped
because atttypid will be set to zero. But the latter is just a
defense measure in case somebody forgets to check attisdropped;
you're not supposed to forget that.
regards, tom lane
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To: pgsql-bugs@postgresql.org
Cc: tgl@sss.pgh.pa.us, tomas.vondra@2ndquadrant.com, andres@anarazel.de, buschmann@nidsa.net, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #16045: vacuum_db crash and illegal memory alloc after pg_upgrade from PG11 to PG12
In-Reply-To: <27596.1571062600@sss.pgh.pa.us>
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