Horton

Re: Statistics Import and Export

Corey Huinker <corey.huinker@gmail.com>

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From: Corey Huinker <corey.huinker@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Jeff Davis <pgsql@j-davis.com>, Tom Lane <tgl@sss.pgh.pa.us>, 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: 2025-02-24T17:57:17Z
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 Mon, Feb 24, 2025 at 9:54 AM Andres Freund <andres@anarazel.de> wrote:

> Hi,
>
> On 2025-02-24 05:11:48 -0500, Corey Huinker wrote:
> > Incorporating most of the feedback (I kept a few of
> > the appendNamedArgument() calls)  presented over the weekend.
> >
> > * removeVersionNumStr is gone
> > * relpages/reltuples/relallvisible are now char[32] buffers in
> RelStatsInfo
> > and nowhere else (existing relpages conversion remains, however)
>
> I don't see the point. This will use more memory and if we can't get
> conversions between integers and strings right we have much bigger
> problems. The same code was used in the backend too!
>

As I see it, the point is that we're getting an input that is a string
representation from the query, and the end-goal is to convey that value
with fidelity to the destination database, so there's nothing we can do to
get us closer to the string that we already have.

I don't have benchmark numbers beyond the instinct that doing something
takes more time than doing nothing. Granted, "nothing" here means 96 bytes
of memory and 3 strncpy()s, and "something" is 24 bytes of memory, 2
atoi()s, 1 strtof() plus whatever memory and processing we do back in
converting back to strings.


> And it leads to storing relpages in two places, with different
> transformations, which doesn't seem great.
>

I didn't like that either, but balanced the ugliness of that vs the cost of
grinding the values back to where we started.


>
>
> > @@ -6921,6 +6927,7 @@ getTables(Archive *fout, int *numTables)
> >       appendPQExpBufferStr(query,
> >                                                "SELECT c.tableoid,
> c.oid, c.relname, "
> >                                                "c.relnamespace,
> c.relkind, c.reltype, "
> > +                                              "c.relpages, c.reltuples,
> c.relallvisible, "
> >                                                "c.relowner, "
> >                                                "c.relchecks, "
> >                                                "c.relhasindex,
> c.relhasrules, c.relpages, "
>
> That query is already querying relpages a bit later in the query, so we'd
> query the column twice.
>

+1, must eliminate that duplicate.


>
>
>
> > +     printfPQExpBuffer(query, "EXECUTE getAttributeStats(");
> > +     appendStringLiteralAH(query, dobj->namespace->dobj.name, fout);
> > +     appendPQExpBufferStr(query, ", ");
> > +     appendStringLiteralAH(query, dobj->name, fout);
> > +     appendPQExpBufferStr(query, "); ");
> >       res = ExecuteSqlQuery(fout, query->data, PGRES_TUPLES_OK);
>
> It seems somewhat ugly that we're building an SQL string with non-trivial
> constants. It'd be better to use PQexecParams() - but I guess we don't have
> any uses of it yet in pg_dump.
>

+1, I would like to see that change.


>
> ISTM that we ought to expose the relation oid in pg_stats. This query
> would be
> simpler and faster if we could just use the oid as the predicate. Will
> take a
> while till we can rely on that, but still.
>

+1, but we will need to support this until v18 is as old as v9.2 is
now...approx 2038.


> Have you compared performance of with/without stats after these
> optimizations?


I have not.