From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Teodor Sigaev <teodor(at)sigaev(dot)ru> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | GenericXLogUnregister seems like a pretty horrid idea |
Date: | 2016-04-09 18:15:44 |
Message-ID: | 17980.1460225744@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
I've been doing some code review in generic_xlog.c, and I find that
GenericXLogUnregister is implemented in what seems to me to be a
completely unsafe way: it shoves over the per-page array entries for
following pages. The problem with that is that it invalidates the Page
pointers previously returned for those pages by GenericXLogRegister;
an effect that is neither documented, nor reasonable for callers to
cope with.
I cannot see any very good reason why callers should need an unregister
function anyway: if they're doing something so complicated that they might
change their minds partway through an XLOG record through about whether a
page needs to be modified, that code is badly in need of redesign. (And
yes, I am asserting that against blinsert() in particular. That's not
nice code.)
I think we should get rid of this function. If people need to do
something like that, they should do GenericXLogAbort() and start over.
regards, tom lane
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