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Re: Avoid orphaned objects dependencies, take 3

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

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From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Michael Paquier <michael@paquier.xyz>, Alexander Lakhin <exclusion@gmail.com>, pgsql-hackers@lists.postgresql.org, Tom Lane <tgl@sss.pgh.pa.us>
Date: 2024-06-26T10:24:41Z
Lists: pgsql-hackers

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Hi,

On Fri, Jun 21, 2024 at 01:22:43PM +0000, Bertrand Drouvot wrote:
> Another thought for the RelationRelationId class case: we could check if there
> is a lock first and if there is no lock then acquire one. That way that would
> ensure the relation is always locked (so no "risk" anymore), but OTOH it may
> add "unecessary" locking (see 2. mentioned previously).

Please find attached v12 implementing this idea for the RelationRelationId class
case. As mentioned, it may add unnecessary locking for 2. but I think that's
worth it to ensure that we are always on the safe side of thing. This idea is
implemented in LockNotPinnedObjectById().

A few remarks:

- there is one place where the relation is not visible (even if
CommandCounterIncrement() is used). That's in TypeCreate(), because the new 
relation Oid is _not_ added to pg_class yet.
Indeed, in heap_create_with_catalog(), AddNewRelationType() is called before
AddNewRelationTuple()). I put a comment in this part of the code explaining why
it's not necessary to call LockRelationOid() here.

- some namespace related stuff is removed from "test_oat_hooks/expected/alter_table.out".
That's due to the logic in cachedNamespacePath() and the fact that the same
namespace related stuff is added prior in alter_table.out.

- the patch touches 37 .c files, but that's mainly due to the fact that
LockNotPinnedObjectById() has to be called in a lot of places.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com

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  1. Avoid orphaned objects dependencies

  2. Don't try to record dependency on a dropped column's datatype