Horton

Re: race condition in pg_class

Grigory Smolkin <smallkeen@gmail.com>

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From: Smolkin Grigory <smallkeen@gmail.com>
To: pgsql-hackers@postgresql.org
Date: 2023-10-27T10:03:23Z
Lists: pgsql-hackers

Commits

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  1. Replace tests of ALTER DATABASE RESET TABLESPACE.

  2. meson: Flush stdout in testwrap

  3. Fix catcache invalidation of a list entry that's being built

  4. Stop reading uninitialized memory in heap_inplace_lock().

  5. Fix use of uninitialized value in previous commit.

  6. Back-patch "Refactor code in tablecmds.c to check and process tablespace moves"

  7. Fix data loss at inplace update after heap_update().

  8. For inplace update durability, make heap_update() callers wait.

  9. Warn if LOCKTAG_TUPLE is held at commit, under debug_assertions.

  10. Don't lose partitioned table reltuples=0 after relhassubclass=f.

  11. Fix new assertion for MERGE view_name ... DO NOTHING.

  12. Remove configuration-dependent output from new inplace-inval test.

  13. AccessExclusiveLock new relations just after assigning the OID.

  14. Cope with inplace update making catcache stale during TOAST fetch.

  15. Expand comments and add an assertion in nodeModifyTable.c.

  16. Improve test coverage for changes to inplace-updated catalogs.

  17. Lock before setting relhassubclass on RELKIND_PARTITIONED_INDEX.

  18. Lock owned sequences during ALTER TABLE SET { LOGGED | UNLOGGED }.

  19. Make TAP todo_start effects the same under Meson and prove_check.

  20. Add an injection_points isolation test suite.

  21. Add wait event type "InjectionPoint", a custom type like "Extension".

  22. Create waitfuncs.c for pg_isolation_test_session_is_blocked().

  23. Rework planning and execution of UPDATE and DELETE.

> This is going to be a problem with any operation that does a transactional
> pg_class update without taking a lock that conflicts with ShareLock.
GRANT
> doesn't lock the table at all, so I can reproduce this in v17 as follows:
>
> == session 1
> create table t (c int);
> begin;
> grant select on t to public;
>
> == session 2
> alter table t add primary key (c);
>
> == back in session 1
> commit;
>
>
> We'll likely need to change how we maintain relhasindex or perhaps take a
lock
> in GRANT.

Oh, that explains it. Thank you very much.

> Can you explore that as follows?
>
>- PITR to just before the COMMIT record.
>- Save all rows of pg_class.
>- PITR to just after the COMMIT record.
>- Save all rows of pg_class.
>- Diff the two sets of saved rows.

Sure, but it will take some time, its a large db with lots of WAL segments
to apply.

> extensions

      extname       | extversion
--------------------+------------
 plpgsql            | 1.0
 pg_stat_statements | 1.8
 pg_buffercache     | 1.3
 pgstattuple        | 1.5