Horton

Re: Compilation issues for HASH_STATISTICS and HASH_DEBUG options

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>
Cc: "'pgsql-hackers@lists.postgresql.org'" <pgsql-hackers@lists.postgresql.org>
Date: 2025-08-14T14:00:37Z
Lists: pgsql-hackers 
"Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com> writes:
> I found that postgres could not be built if a complier option HASH_STATISTICS is
> set [1]. Also, I found HASH_DEBUG option caused warnings [2]. Usage of the are
> mentioned at the code comments in dynahash.c.

> I'm not sure whether we would keep supporting them because no one may not have
> used anymore now.

Ugh.  I did a bit of "git bisect" work and discovered that:

1.  HASH_DEBUG got broken at

commit 44ca4022f3f9297bab5cbffdd97973dbba1879ed
Author: Robert Haas <rhaas@postgresql.org>
Date:   Wed Mar 23 10:56:23 2016 -0400

    Partition the freelist for shared dynahash tables.

and was fixed again at

commit 9d4e56699957b261390c50dcda7f947470017484
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date:   Wed Aug 2 12:16:50 2017 -0400

    Remove broken and useless entry-count printing in HASH_DEBUG code.

and then broke again at

commit be0a6666656ec3f68eb7d8e7abab5139fcd47012
Author: Thomas Munro <tmunro@postgresql.org>
Date:   Sat Sep 19 11:28:34 2020 +1200

    Remove large fill factor support from dynahash.c.

2.  HASH_STATISTICS got broken at

commit cc5ef90edd809eaf85e11a0ee251229bbf7ce798
Author: Michael Paquier <michael@paquier.xyz>
Date:   Fri Mar 15 07:57:17 2024 +0900

    Refactor initial hash lookup in dynahash.c


Based on this, I think we should remove the HASH_DEBUG support.
It's been broken for six of the last nine years and only one
person ever noticed.  Moreover, if you were trying to find a
problem in dynahash, you'd probably want different debug logging
than what's here.

There might be a case for removing HASH_STATISTICS too, but
it seems weaker.  I do recall having made use of that code
once years ago ...

			regards, tom lane

Commits

  1. Remove HASH_DEBUG output from dynahash.c

  2. Use elog(DEBUG4) for dynahash.c statistics output

  3. Fix invalid format string in HASH_DEBUG code

  4. Fix failing -D HASH_STATISTICS builds

  5. Refactor initial hash lookup in dynahash.c

  6. Remove large fill factor support from dynahash.c.

  7. Remove broken and useless entry-count printing in HASH_DEBUG code.

  8. Partition the freelist for shared dynahash tables.