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: Alexander Lakhin <exclusion@gmail.com>, Robert Haas <robertmhaas@gmail.com>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>, pgsql-hackers@postgresql.org
Date: 2023-10-26T05:06:23Z
Lists: pgsql-hackers 
On Thu, 2023-10-26 at 07:00 +0300, Alexander Lakhin wrote:

> It looks like the buffer is not dirty in the problematic call.

Thank you for the report! I was able to reproduce and observe that the
buffer is not marked dirty.

The call (hashovfl.c:671):

  XLogRegisterBuffer(1, wbuf, REGBUF_STANDARD)

is followed unconditionally by:

  PageSetLSN(BufferGetPage(wbuf), recptr)

so if the Assert were not there, it would be setting the LSN on a page
that's not marked dirty. Therefore I think this is a bug, or at least
an interesting/unexpected case.

Perhaps the registration and the PageSetLSN don't need to happen when
nitups==0?

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.