Horton

Re: Is this a problem in GenericXLogFinish()?

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, Alexander Lakhin <exclusion@gmail.com>, Robert Haas <robertmhaas@gmail.com>, Jeff Davis <pgsql@j-davis.com>, Heikki Linnakangas <hlinnaka@iki.fi>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2024-04-10T09:58:22Z
Lists: pgsql-hackers 
On Wed, Apr 10, 2024 at 1:27 PM Michael Paquier <michael@paquier.xyz> wrote:
>
> On Tue, Apr 09, 2024 at 10:25:36AM +0000, Hayato Kuroda (Fujitsu) wrote:
> >> On Fri, Apr 05, 2024 at 06:22:58AM +0000, Hayato Kuroda (Fujitsu) wrote:
> >> I'm slightly annoyed by the fact that there is no check on
> >> is_prim_bucket_same_wrt for buffer 1 in the BLK_NEEDS_REDO case to
> >> show the symmetry between the insert and replay paths.  Shouldn't
> >> there be at least an assert for that in the branch when there are no
> >> tuples (imagine an else to cover xldata->ntups == 0)?  I mean between
> >> just before updating the hash page's opaque area when
> >> is_prev_bucket_same_wrt.
> >
> > Indeed, added an Assert() in else part. Was it same as your expectation?
>
> Yep, close enough.  Thanks to the insert path we know that there will
> be no tuples if (is_prim_bucket_same_wrt || is_prev_bucket_same_wrt),
> and the replay path where the assertion is added.
>

It is fine to have an assertion for this path.

+ else
+ {
+ /*
+ * See _hash_freeovflpage() which has a similar assertion when
+ * there are no tuples.
+ */
+ Assert(xldata->is_prim_bucket_same_wrt ||
+    xldata->is_prev_bucket_same_wrt);

I can understand this comment as I am aware of this code but not sure
it would be equally easy for the people first time looking at this
code. One may try to find the equivalent assertion in
_hash_freeovflpage(). The alternative could be: "Ensure that the
required flags are set when there are no tuples. See
_hash_freeovflpage().". I am also fine if you prefer to go with your
proposed comment.

Otherwise, the patch looks good to me.

-- 
With Regards,
Amit Kapila.

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.