Re: [COMMITTERS] pgsql: Fix bufmgr so CHECKPOINT_END_OF_RECOVERY behaves as a shutdown c

On Mon, Sep 17, 2012 at 11:14 AM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> I just noted during investigating of the impact of the fakerelcache bug that
> contrary to whats claimed at several places END_OF_RECOVERY checkpoints do
> *not* behave the same way CHECKPOINT_IS_SHUTDOWN ones do. Which doesn't seem to
> be a good idea. E.g. the impact of this bug would have been smaller if they
> were really treated the same. Unless I missed something thats the only place of
> relevance that treats them differently.
> Imo treating them different in some remote places (2 calls away) is a good way
> to introduce further bugs.

OK, I can agree with that. As a backstop against future mistakes, it
makes some sense to me.

>> Maybe what we should do is - if this is an end-of-recovery checkpoint
>> - *assert* that the BM_PERMANENT bit is set on every buffer we find.
>> That would provide a useful cross-check that we don't have a bug
>> similar to the one Jeff already fixed in any other code path.
> I haven't looked into the details, but can't a new unlogged relation be created
> since the last checkpoint and thus have pages in s_b?

Data changes to unlogged relations are not WAL-logged, so there's no
reason for recovery to ever read them. Even if such a reason existed,
there wouldn't be anything to read, because the backing files are
unlinked before WAL replay begins.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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