Horton

Re: Schema variables - new implementation for Postgres 15

Pavel Stehule <pavel.stehule@gmail.com>

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From: Pavel Stehule <pavel.stehule@gmail.com>
To: Julien Rouhaud <rjuju123@gmail.com>
Cc: Dean Rasheed <dean.a.rasheed@gmail.com>, Joel Jacobson <joel@compiler.org>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-01-25T08:35:09Z
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. Allow underscores in integer and numeric constants.

  2. Remove special outfuncs/readfuncs handling of RangeVar.catalogname.

  3. Remove extra space from dumped ALTER DEFAULT PRIVILEGES.

  4. Create FKs properly when attaching table as partition

  5. psql: improve tab-complete's handling of variant SQL names.

út 25. 1. 2022 v 6:18 odesílatel Julien Rouhaud <rjuju123@gmail.com> napsal:

> Hi,
>
> On Mon, Jan 24, 2022 at 12:33:11PM +0100, Pavel Stehule wrote:
> >
> > here is updated patch with locking support
>
> Thanks for updating the patch!
>
> While the locking is globally working as intended, I found a few problems
> with
> it.
>
> First, I don't think that acquiring the lock in
> get_session_variable_type_typmod_collid() and
> prepare_variable_for_reading() is
> the correct approach.  In transformColumnRef() and transformLetStmt() you
> first
> call IdentifyVariable() to check if the given name is a variable without
> locking it and later try to lock the variable if you get a valid Oid.
> This is
> bug prone as any other backend could drop the variable between the two
> calls
> and you would end up with a cache lookup failure.  I think the lock should
> be
> acquired during IdentifyVariable.  It should probably be optional as one
> codepath only needs the information to raise a warning when a variable is
> shadowed, so a concurrent drop isn't a problem there.
>

There is a problem, because before the IdentifyVariable call I don't know
if the variable will be shadowed or not.

If I lock a variable inside IdentifyVariable, then I need to remember if I
did lock there, or if the variable was locked already, and If the variable
is shadowed and if lock is fresh, then I can unlock the variable.


Regards

Pavel