Horton

Re: Statistics Import and Export

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Corey Huinker <corey.huinker@gmail.com>
Cc: Nathan Bossart <nathandbossart@gmail.com>, Jeff Davis <pgsql@j-davis.com>, Tom Lane <tgl@sss.pgh.pa.us>, Michael Paquier <michael@paquier.xyz>, jian he <jian.universality@gmail.com>, Bruce Momjian <bruce@momjian.us>, Matthias van de Meent <boekewurm+postgres@gmail.com>, Magnus Hagander <magnus@hagander.net>, Stephen Frost <sfrost@snowman.net>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, Peter Smith <smithpb2250@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, alvherre@alvh.no-ip.org
Date: 2025-03-06T17:16:28Z
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.

Hi,

On 2025-03-06 12:04:25 -0500, Corey Huinker wrote:
> > > If there's value in freeing them, why isn't it being done already? What
> > > other thing would consume this freed memory?
> >
> > I'm not saying that they can be freed, they can't right now. My point is
> > just
> > that we *already* keep all the stats in memory, so the fact that fetching
> > all
> > stats in a single query would also require keeping them in memory is not an
> > issue.
> >
> 
> That's true in cases where we're not filtering schemas or tables. We fetch
> the pg_class stats as a part of getTables, but those are small, and not a
> part of the query in question.
> 
>  Fetching all the pg_stats for a db when we only want one table could be a
> nasty performance regression

I don't think anybody argued that we should fetch all stats regardless of
filtering for the to-be-dumped tables.


> and we can't just filter on the oids of the tables we want, because those
> tables can have expression indexes, so the oid filter would get complicated
> quickly.

I don't follow. We already have the tablenames, schemanames and oids of the
to-be-dumped tables/indexes collected in pg_dump, all that's needed is to send
a list of those to the server to filter there?


> > But TBH, I do wonder how much the current memory usage of the statistics
> > dump/restore support is going to bite us. In some cases this will
> > dramatically
> > increase pg_dump/pg_upgrade's memory usage, my tests were with tiny
> > amounts of
> > data and very simple scalar datatypes and you already could see a
> > substantial
> > increase.  With something like postgis or even just a lot of jsonb columns
> > this is going to be way worse.
> >
> 
> Yes, it will cost us in pg_dump, but it will save customers from some long
> ANALYZE operations.

My concern is that it might prevent some upgrades from *ever* completing,
because of pg_dump running out of memory.

Greetings,

Andres Freund