Horton

RE: Statistics Import and Export

Shinoda, Noriyoshi <noriyoshi.shinoda@hpe.com>

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From: "Shinoda, Noriyoshi (SXD Japan FSIP)" <noriyoshi.shinoda@hpe.com>
To: Jeff Davis <pgsql@j-davis.com>, jian he <jian.universality@gmail.com>, Corey Huinker <corey.huinker@gmail.com>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>, Bruce Momjian <bruce@momjian.us>, Tom Lane <tgl@sss.pgh.pa.us>, Nathan Bossart <nathandbossart@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>, Tomas Vondra <tomas.vondra@enterprisedb.com>, "alvherre@alvh.no-ip.org" <alvherre@alvh.no-ip.org>
Date: 2024-10-12T13:02:55Z
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.

Attachments

Hi,
Thank you for developing this great feature. I have tested the committed feature. 
The manual for the pg_set_relation_stats function says the following:
  "The value of relpages must be greater than or equal to 0"

However, this function seems to accept -1 for the relpages parameter. Below is an example of execution:
---
postgres=> CREATE TABLE data1(c1 INT PRIMARY KEY, c2 VARCHAR(10));
CREATE TABLE
postgres=> SELECT pg_set_relation_stats('data1', relpages=>-1);
 pg_set_relation_stats
-----------------------
 t
(1 row)
postgres=> SELECT relname, relpages FROM pg_class WHERE relname='data1';
 relname | relpages
---------+----------
 data1   |       -1
(1 row)
---

The attached patch modifies the pg_set_relation_stats function to work as described in the manual.

Regards,
Noriyoshi Shinoda

-----Original Message-----
From: Jeff Davis <pgsql@j-davis.com> 
Sent: Saturday, October 12, 2024 8:11 AM
To: jian he <jian.universality@gmail.com>; Corey Huinker <corey.huinker@gmail.com>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>; Bruce Momjian <bruce@momjian.us>; Tom Lane <tgl@sss.pgh.pa.us>; Nathan Bossart <nathandbossart@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>; Tomas Vondra <tomas.vondra@enterprisedb.com>; alvherre@alvh.no-ip.org
Subject: Re: Statistics Import and Export

On Mon, 2024-09-23 at 08:57 +0800, jian he wrote:
>     newtup = heap_modify_tuple_by_cols(ctup, tupdesc, ncols, replaces, 
> nulls);
> 
> you just directly declared "bool nulls[3]    = {false, false, false};"

Those must be false (not NULL), because in pg_class those are non-NULL attributes. They must be set to something whenever we update.

> if any of (RELPAGES_ARG, RELTUPLES_ARG, RELALLVISIBLE_ARG) is null, 
> should you set that null[position] to true?

If the corresponding SQL argument is NULL, we leave the existing value unchanged, we don't set it to NULL.

> otherwise, i am confused with the variable nulls.
> 
> Looking at other usage of heap_modify_tuple_by_cols, "ncols" cannot be 
> dynamic, it should be a fixed value?
> The current implementation works, because the (bool[3] nulls) is 
> always false, never changed.
> if nulls becomes {false, false, true} then "ncols" must be 3, cannot 
> be 2.

heap_modify_tuple_by_cols() uses ncols to specify the length of the values/isnull arrays. The "replaces" is an array of attribute numbers to replace (in contrast to plain heap_modify_tuple(), which uses an array of booleans).

We are going to replace a maximum of 3 attributes, so the arrays have a maximum size of 3. Predeclaring the arrays to be 3 elements is just fine even if we only use the first 1-2 elements -- it avoids a needless heap allocation/free.

Regards,
	Jeff Davis