Horton

Re: Statistics Import and Export

Magnus Hagander <magnus@hagander.net>

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From: Magnus Hagander <magnus@hagander.net>
To: Jeff Davis <pgsql@j-davis.com>
Cc: Greg Sabino Mullane <htamfids@gmail.com>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, Corey Huinker <corey.huinker@gmail.com>, Andres Freund <andres@anarazel.de>, Tom Lane <tgl@sss.pgh.pa.us>, Michael Paquier <michael@paquier.xyz>, Nathan Bossart <nathandbossart@gmail.com>, Bruce Momjian <bruce@momjian.us>, Matthias van de Meent <boekewurm+postgres@gmail.com>, Stephen Frost <sfrost@snowman.net>, Peter Smith <smithpb2250@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, alvherre@alvh.no-ip.org, jian he <jian.universality@gmail.com>
Date: 2025-03-02T14:38:07Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Change pg_dump default for statistics export.

  2. pg_dump: Adjust reltuples from 0 to -1 for dumps of older versions.

  3. vacuumdb: Don't skip empty relations in --missing-stats-only mode.

  4. pg_dump: Fix query for gathering attribute stats on older versions.

  5. Prevent redeclaration of typedef TocEntry.

  6. Remove unused function parameters in pg_backup_archiver.c.

  7. pg_dump: Retrieve attribute statistics in batches.

  8. pg_dump: Reduce memory usage of dumps with statistics.

  9. Skip second WriteToc() call for custom-format dumps without data.

  10. Add relallfrozen to pg_dump statistics.

  11. Matview statistics depend on matview data.

  12. Add pg_dump --with-{schema|data|statistics} options.

  13. Stats: use schemaname/relname instead of regclass.

  14. CREATE INDEX: do update index stats if autovacuum=off.

  15. Don't convert to and from floats in pg_dump.

  16. CREATE INDEX: don't update table stats if autovacuum=off.

  17. Organize and deduplicate statistics import tests.

  18. Address stats export review comments.

  19. Address stats import review comments.

  20. Add relallfrozen to pg_class

  21. Fix pg_strtof() to not crash on NULL endptr.

  22. Use attnum to identify index columns in pg_restore_attribute_stats().

  23. pg_dump: prepare attribute stats query.

  24. Avoid unnecessary relation stats query in pg_dump.

  25. Remove redundant pg_set_*_stats() variants.

  26. Do not use in-place updates for statistics import.

  27. Fix confusion about data type of pg_class.relpages and relallvisible.

  28. Documentation fixups for dumping statistics.

  29. Trial fix for old cross-version upgrades.

  30. Transfer statistics during pg_upgrade.

  31. Lock table in ShareUpdateExclusive when importing index stats.

  32. Use in-place updates for pg_restore_relation_stats().

  33. Improve error message for replication of generated columns.

  34. pg_dump: Add dumpSchema and dumpData derivative flags.

  35. Disallow modifying statistics on system columns.

  36. Add missing CommandCounterIncrement() in stats import functions.

  37. Add functions pg_restore_relation_stats(), pg_restore_attribute_stats().

  38. Documentation fixup.

  39. Add functions pg_set_attribute_stats() and pg_clear_attribute_stats().

  40. Change pg_*_relation_stats() functions to return type to void.

  41. Disable autovacuum for tables in stats import tests.

  42. Allow pg_set_relation_stats() to set relpages to -1.

  43. Fixup for pg_set_relation_stats().

  44. Create functions pg_set_relation_stats, pg_clear_relation_stats.

  45. Add memory/disk usage for Window aggregate nodes in EXPLAIN.

  46. Improve performance of dumpSequenceData().

  47. Add INJECTION_POINT_CACHED() to run injection points directly from cache

  48. Improve performance of binary_upgrade_set_pg_class_oids().

  49. Improve assertion in mdwritev()

  50. CREATE INDEX: do not update stats during binary upgrade.

  51. Redefine pg_class.reltuples to be -1 before the first VACUUM or ANALYZE.

On Sat, Mar 1, 2025 at 9:48 PM Jeff Davis <pgsql@j-davis.com> wrote:

> On Sat, 2025-03-01 at 13:52 -0500, Greg Sabino Mullane wrote:
> > > Can you expand on some of those cases?
> >
> > Certainly. I think one of the problems is that because this patch is
> > solving a pg_upgrade issue, the focus is on the "dump and restore"
> > scenarios. But pg_dump is used for much more than that, especially
> > "dump and examine".
>
> Thank you for going through these examples.
>
> > I just don't think it should be enabled by default for everything
> > using pg_dump. For the record, I would not strongly object to having
> > stats on by default for binary dumps, although I would prefer them
> > off.
>
> I am open to that idea, I just want to get it right, because probably
> whatever the default is in 18 will stay that way.
>
> Also, we will need to think through the set of pg_dump options again. A
> lot of our tools seem to assume that "if it's the default, we don't
> need a way to ask for it explicitly", which makes it a lot harder to
> ever change the default and keep a coherent set of options.
>

That's a good point in general, and definitely something we should think
through, independently of his patch.


> > So why not just expect people to modify their programs to use --no-
> > statistics for cases like this? That's certainly an option, but it's
> > going to break a lot of existing things, and create branching code:
>
> I suggest that we wait a bit to see what additional feedback we get
> early in beta.
>

I definitely thing it should be on by default.

FWIW, I've seen many cases of people using automated tools to verify the
*schema* between two databases. I'd say that's quite common. But they use
pg_dump -s, which I believe is not affected by this one.

I don't think I've ever come across an automated tool to verify the
contents of an entire database this way. That doesn't mean it's not out
there of course, just that it's not so common. The cases I've seen pg_dump
used to verify the contents that's always been in combination with a myriad
of other switches such as include/exclude of specific tables etc, and
adding just one more switch to those seems like a small price to pay for
having the default behaviour be a big improvement for the majority of
usecases.


> Also, anything trained to parse pg_dump output will have to learn
> > about the new SELECT pg_restore_ calls with their multi-line formats
> > (not 100% sure we don't have that anywhere, as things like "SELECT
> > setval" and "SELECT set_config" are single line, but there may be
> > existing things)
>

That's going to be true every time we add something to pg_dump. And for
that matter, anything new to *postgresql*, since surely we'd want pg_dump
to dump objects by default. Any tool that parses the pg_dump output
directly will always have to carefully analyze each new version. And
probably shouldn't be using the plaintext format in the first place - and
if using pg_restore it comes out as it's own type of object, making it easy
to exclude at that level.

--
 Magnus Hagander
 Me: https://www.hagander.net/ <http://www.hagander.net/>
 Work: https://www.redpill-linpro.com/ <http://www.redpill-linpro.com/>