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From: Tom Lane <[email protected]>
To: Egor Rogov <[email protected]>
Cc: [email protected]
Subject: Re: FrozenTransactionId
Date: Tue, 06 Sep 2016 16:41:39 -0400
Message-ID: <[email protected]> (raw)
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Egor Rogov <[email protected]> writes:
> Right, it does not say that FrozenTransactionId is what appears on disk, 
> but what is? There is no such information anywhere in the doc. Since 9.4 
> frozen transactions have their normal XIDs preserved, so how a user can 
> tell normal transaction from frozen one? This is what needs to be 
> explained, I believe.

I'm afraid the answer is "you can't tell".  The infomask bits in tuple
headers aren't exposed via SQL.  If you're really desperate,
contrib/pageinspect would help, but I don't propose mentioning that here.

In general, I'm not really sure why users would care very much at
a tuple-by-tuple level.  Aggregate statistics would be interesting,
which raises the question why contrib/pgstattuple doesn't provide
frozen-tuples counts.

			regards, tom lane


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