Horton

Re: Is this a problem in GenericXLogFinish()?

Jeff Davis <pgsql@j-davis.com>

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From: Jeff Davis <pgsql@j-davis.com>
To: Heikki Linnakangas <hlinnaka@iki.fi>, Robert Haas <robertmhaas@gmail.com>
Cc: pgsql-hackers@postgresql.org
Date: 2023-10-10T19:57:35Z
Lists: pgsql-hackers

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I committed and backported 0001 (the GenericXLogFinish() fix but not
the Assert).

Strangely I didn't see the -committers email come through yet. If
anyone notices anything wrong, please let me know before the final v11
release.

On Thu, 2023-09-28 at 12:05 -0700, Jeff Davis wrote:
> Also, I ran into some problems with GIN that might require a bit more
> refactoring in ginPlaceToPage(). Perhaps we could consider
> REGBUF_NO_CHANGE a general bypass of the Assert(BufferIsDirty()), and
> use it temporarily until we have a chance to analyze/refactor each of
> the callers that need it.

For the Assert, I have attached a new patch for v17.

I changed the name of the flag to REGBUF_CLEAN_OK, because for some of
the callsites it was not clear to me whether the page is always
unchanged or sometimes unchanged. In other words, REGBUF_CLEAN_OK is a
way to bypass the Assert for callsites where we either know that we
actually want to register an unchanged page, or for callsites where we
don't know if the page is changed or not.

If we commit this, ideally someone would look into the places where
REGBUF_CLEAN_OK is used and make sure that it's not a bug, and perhaps
refactor so that it would benefit from the Assert. But refactoring
those places is outside of the scope of this patch.

It sounds like we have no intention to change the hash index code, so
are we OK if this flag just lasts forever? Do you still think it offers
a useful check?

Regards,
	Jeff Davis

Commits

  1. Fix inconsistency with replay of hash squeeze record for clean buffers

  2. Set LSN for wbuf in _hash_freeovflpage() iff wbuf is modified.

  3. Fix an uninitialized access in hash_xlog_squeeze_page().

  4. Use REGBUF_NO_CHANGE at one more place in the hash index.

  5. Assert that buffers are marked dirty before XLogRegisterBuffer().

  6. Fix bug in GenericXLogFinish().

  7. Improve hash index bucket split behavior.