Horton

Re: race condition in pg_class

Noah Misch <noah@leadboat.com>

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From: Noah Misch <noah@leadboat.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: Robert Haas <robertmhaas@gmail.com>, pgsql-hackers@postgresql.org, Tom Lane <tgl@sss.pgh.pa.us>, Smolkin Grigory <smallkeen@gmail.com>
Date: 2024-06-14T02:42:25Z
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. 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.

On Fri, Jun 14, 2024 at 09:58:59AM +0900, Michael Paquier wrote:
> Looking at inplace031-inj-wait-event..
> 
> The comment at the top of GetWaitEventCustomNames() requires an
> update, still mentioning extensions.

Thanks.  Fixed locally.

> GetWaitEventCustomIdentifier() is incorrect, and should return
> "InjectionPoint" in the default case of this class name, no?

I intentionally didn't provide a default event ID for InjectionPoint.
PG_WAIT_EXTENSION needs a default case for backward compatibility, if nothing
else.  For this second custom type, it's needless complexity.  The value
0x0B000000U won't just show up like PG_WAIT_EXTENSION does.
GetLWLockIdentifier() also has no default case.  How do you see it?

> I would
> just pass the classID to GetWaitEventCustomIdentifier().

As you say, that would allow eventId==0 to raise "could not find custom wait
event" for PG_WAIT_INJECTIONPOINT instead of wrongly returning "Extension".
Even if 0x0B000000U somehow does show up, having pg_stat_activity report
"Extension" instead of an error, in a developer test run, feels unimportant to
me.

> It is suboptimal to have pg_get_wait_events() do two scans of
> WaitEventCustomHashByName.  Wouldn't it be better to do a single scan,
> returning a set of (class_name,event_name) fed to the tuplestore of
> this SRF?

Micro-optimization of pg_get_wait_events() doesn't matter.  I did consider
that or pushing more of the responsibility into wait_events.c, but I
considered it on code repetition grounds, not performance grounds.

>  uint32
>  WaitEventExtensionNew(const char *wait_event_name)
>  {
> +	return WaitEventCustomNew(PG_WAIT_EXTENSION, wait_event_name);
> +}
> +
> +uint32
> +WaitEventInjectionPointNew(const char *wait_event_name)
> +{
> +	return WaitEventCustomNew(PG_WAIT_INJECTIONPOINT, wait_event_name);
> +}
> 
> Hmm.  The advantage of two routines is that it is possible to control
> the class IDs allowed to use the custom wait events.  Shouldn't the
> second routine be documented in xfunc.sgml?

The patch added to xfunc.sgml an example of using it.  I'd be more inclined to
delete the WaitEventExtensionNew() docbook documentation than to add its level
of detail for WaitEventInjectionPointNew().  We don't have that kind of
documentation for most extension-facing C functions.