Horton

Re: Statistics Import and Export

Tom Lane <tgl@sss.pgh.pa.us>

View thread
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Corey Huinker <corey.huinker@gmail.com>
Cc: Jeff Davis <pgsql@j-davis.com>, 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: 2025-02-26T04:36:09Z
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.

Corey Huinker <corey.huinker@gmail.com> writes:
> My solution so far is to take allo the v11+ (SELECT array_agg...) functions
> and put them into a LATERAL, two of them filtered by attstattarget > 0 and
> a new one aggregating attnames with no filter.

> An alternative would be a new subselect for array_agg(attname) WHERE
> in.indexprs IS NOT NULL, thus removing the extra compute for the indexes
> that lack an index expression (i.e. most of them), and thus lack settable
> stats (at least for now) and wouldn't be affected by the name-jitter issue
> anyway.

Yeah, I've been thinking about that.  I think that the idea of the
current design is that relatively few indexes will have explicit stats
targets set on them, so most of the time the sub-SELECTs produce no
data.  (Which is not to say that they're cheap to execute.)  If we
pull all the column names for all indexes then we'll likely bloat
pg_dump's working storage quite a bit.  Pulling them only for indexes
with expression columns should fix that, and as you say we don't need
the names otherwise.

I still fear that those sub-selects are pretty expensive in aggregate
-- they are basically forcing a nestloop join -- and maybe we need to
rethink that whole idea.

BTW, just as a point of order: it is not the case that non-expression
indexes are free of name-jitter problems.  That's because we don't
bother to rename index columns when the underlying table column is
renamed, thus:

regression=# create table t1 (id int primary key);
CREATE TABLE
regression=# \d t1_pkey
        Index "public.t1_pkey"
 Column |  Type   | Key? | Definition 
--------+---------+------+------------
 id     | integer | yes  | id
primary key, btree, for table "public.t1"

regression=# alter table t1 rename column id to xx;
ALTER TABLE
regression=# \d t1_pkey
        Index "public.t1_pkey"
 Column |  Type   | Key? | Definition 
--------+---------+------+------------
 id     | integer | yes  | xx
primary key, btree, for table "public.t1"

After dump-n-reload, this index's column will be named "xx".
That's not relevant to our current problem as long as we
don't store stats on such index columns, but it's plenty
relevant to the ALTER INDEX ... SET STATISTICS code.

> I'm on the fence about how to handle pg_clear_attribute_stats(), leaning
> toward overloaded functions.

I kinda felt that we didn't need to bother with an attnum-based
variant of pg_clear_attribute_stats(), since pg_dump has no
use for that.  I won't stand in the way if you're desperate to
do it, though.

			regards, tom lane