Re: Subtraction carry bug in xlog.c in 7.3 and 7.4 - Mailing list pgsql-hackers

From Tom Lane
Subject Re: Subtraction carry bug in xlog.c in 7.3 and 7.4
Date
Msg-id 17802.1056118498@sss.pgh.pa.us
Whole thread Raw
In response to Subtraction carry bug in xlog.c in 7.3 and 7.4  ("J.R. Nield" <jrnield@usol.com>)
Responses Re: Subtraction carry bug in xlog.c in 7.3 and 7.4
List pgsql-hackers
"J.R. Nield" <jrnield@usol.com> writes:
> The attached patches against 7.3 and 7.4 fix a subtraction carry bug in
> xlog.c.

This is simply a waste of cycles, because xrecoff can never be zero
(if it were, it'd be pointing at a page header, which is not a valid
record location).  If you look around in the code, you'll note that
xrecoff==0 is actually used as an invalid-value flag in a couple of
contexts.

Can you point to anyplace where the behavior would change?  If so
I think there's a deeper bug to fix.

            regards, tom lane

pgsql-hackers by date:

Previous
From: Tom Lane
Date:
Subject: Re: Access to transaction status
Next
From: Robert Treat
Date:
Subject: Re: Two weeks to feature freeze