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Re: Freezing is not WAL-logged

From: "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: <pgsql-bugs(at)postgresql(dot)org>
Subject: Re: Freezing is not WAL-logged
Date: 2006-10-19 20:29:51
Message-ID: 4537E03F.9060606@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-bugs
Tom Lane wrote:
> "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com> writes:
>> I just noticed that freezing a tuple (in vacuumlazy.c) is not 
>> WAL-logged.
> 
> The theory is that this doesn't matter because the tuple is committed
> either way ... it's equivalent to a hint-bit update which we don't
> WAL-log either.

Because the relminxid-update is WAL-logged, you can get into situation 
where relminxid > the real smallest xid of the table, as demonstrated by 
the example I gave. relminxid is used to determine the safe clog cut-off 
point, so that's not harmless.

Granted, the chances of getting data corruption from this are small, but 
it's possible.

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

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