Horton

Re: Statistics Import and Export

Stephen Frost <sfrost@snowman.net>

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From: Stephen Frost <sfrost@snowman.net>
To: Corey Huinker <corey.huinker@gmail.com>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>, 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>
Date: 2024-03-12T08:51:34Z
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.

Greetings,

* Corey Huinker (corey.huinker@gmail.com) wrote:
> > > One persistent problem is that there is no _safe equivalent to ARRAY_IN,
> > so
> > > that can always fail on us, though it should only do so if the string
> > > passed in wasn't a valid array input format, or the values in the array
> > > can't coerce to the attribute's basetype.
> >
> > That would happen before we even get to being called and there's not
> > much to do about it anyway.
> 
> Not sure I follow you here. the ARRAY_IN function calls happen once for
> every non-null stavaluesN parameter, and it's done inside the function
> because the result type could be the base type for a domain/array type, or
> could be the type itself. I suppose we could move that determination to the
> caller, but then we'd need to call get_base_element_type() inside a client,
> and that seems wrong if it's even possible.

Ah, yeah, ok, I see what you're saying here and sure, there's a risk
those might ERROR too, but that's outright invalid data then as opposed
to a NULL getting passed in.

> > > Or one compound command
> > >
> > >     SELECT pg_set_relation_stats(t.oid, ...)
> > >          pg_set_attribute_stats(t.oid, 'id'::name, ...),
> > >          pg_set_attribute_stats(t.oid, 'last_name'::name, ...),
> > >          ...
> > >     FROM (VALUES('foo.bar'::regclass)) AS t(oid);
> > >
> > > The second one has the feature that if any one attribute fails, then the
> > > whole update fails, except, of course, for the in-place update of
> > pg_class.
> > > This avoids having an explicit transaction block, but we could get that
> > > back by having restore wrap the list of commands in a transaction block
> > > (and adding the explicit lock commands) when it is safe to do so.
> >
> > Hm, I like this approach as it should essentially give us the
> > transaction block we had been talking about wanting but without needing
> > to explicitly do a begin/commit, which would add in some annoying
> > complications.  This would hopefully also reduce the locking concern
> > mentioned previously, since we'd get the lock needed in the first
> > function call and then the others would be able to just see that we've
> > already got the lock pretty quickly.
> 
> True, we'd get the lock needed in the first function call, but wouldn't we
> also release that very lock before the subsequent call? Obviously we'd be
> shrinking the window in which another process could get in line and take a
> superior lock, and the universe of other processes that would even want a
> lock that blocks us is nil in the case of an upgrade, identical to existing
> behavior in the case of an FDW ANALYZE, and perfectly fine in the case of
> someone tinkering with stats.

No, we should be keeping the lock until the end of the transaction
(which in this case would be just the one statement, but it would be the
whole statement and all of the calls in it).  See analyze.c:268 or
so, where we call relation_close(onerel, NoLock); meaning we're closing
the relation but we're *not* releasing the lock on it- it'll get
released at the end of the transaction.

Thanks!

Stephen