Horton

Re: Statistics Import and Export

Corey Huinker <corey.huinker@gmail.com>

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From: Corey Huinker <corey.huinker@gmail.com>
To: Jeff Davis <pgsql@j-davis.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@anarazel.de>, Michael Paquier <michael@paquier.xyz>, jian he <jian.universality@gmail.com>, Nathan Bossart <nathandbossart@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: 2025-02-24T01:03:45Z
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 Sun, Feb 23, 2025 at 7:22 PM Jeff Davis <pgsql@j-davis.com> wrote:

> On Sat, 2025-02-22 at 00:00 -0500, Corey Huinker wrote:
> >
> > Attached is the first optimization, which gets rid of the pg_class
> > queries entirely, instead getting the same information from the
> > existing queries in getTables and getIndexes.
>
> Attached a revised version. The main changes are that the only struct
> it changes is RelStatsInfo, and it doesn't carry around string values.
>
> IIUC, your version carried around the string values so that there would
> be no conversion; it would hold the string from one result to the next.
> That makes sense, but it seemed to change a lot of struct fields, and
> have unnecessary string copying and memory usage which was not freed.
> Instead, I used float_to_shortest_decimal_buf(), which is what
> float4out() uses, which should be a consistent way to convert the float
> value.
>


If we're fine with giving up on appendNamedArgument() for relstats,
wouldn't we also want to mash these into a single call?

appendPQExpBuffer(out, "\t'relation', '%s'::regclass,\n", qualname);
appendPQExpBuffer(out, "\t'version', '%u'::integer,\n",
      fout->remoteVersion);
appendPQExpBuffer(out, "\t'relpages', '%d'::integer,\n", rsinfo->relpages);
appendPQExpBuffer(out, "\t'reltuples', '%s'::real,\n", reltuples_str);
appendPQExpBuffer(out, "\t'relallvisible', '%d'::integer\n);\n",
      rsinfo->relallvisible);

to:
appendPQExpBuffer(out, "\t'relation', '%s'::regclass"
                       ",\n\t'version', '%u'::integer"
                       ",\n\t'relpages', '%d'::integer"
                       ",\n\t'reltuples', '%s'::real"
                       ",\n\t'relallvisible', '%d'::integer",
                       qualname, fout->remoteVersion, rsinfo->relpages,
                       rsinfo->reltuples_str, rsinfo->relallvisible);
appendPQExpBufferStr(out, "\n);\n");


Also, there's work elsewhere that may add relallfrozen to pg_class, which
would be something we'd want to add depending on the remoteVersion, and
this format will make that change pretty clear.


>
> That meant that we couldn't use appendNamedArgument() as easily, but it
> wasn't helping much in that function anyway, because it was no longer a
> loop.
>

It still served to encapsulate the format of a kwarg pair, but little more,
agreed.


>
> I didn't measure any performance difference between your version and
> mine, but avoiding a few allocations couldn't hurt. It seems to save
> just under 20% on an unoptimized build.
>

Part of me thinks we'd want to do the reverse - change the struct to store
char[32] to for each of relpages, reltuples, and relallvisible, and then
convert reltpages to int in the one place where we actually need to use in
its numeric form, and even then only in one place. Conversions to and from
other data types introduce the possibility, though very remote, of the
converted-and-then-unconverted value being cosmetically different from what
we got from the server, and if down the road we're dealing with more
complex data types, those conversions might become significant.