Re: [HACKERS] proposal: schema variables

út 4. 9. 2018 v 9:21 odesílatel Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>
napsal:

> AFAICS this patch does nothing to consider parallel safety -- that is,
> as things stand, a variable is allowed in a query that may be
> parallelised, but its value is not copied to workers, leading to
> incorrect results. For example:
>
> create table foo(a int);
> insert into foo select * from generate_series(1,1000000);
> create variable zero int;
> let zero = 0;
>
> explain (costs off) select count(*) from foo where a%10 = zero;
>
> QUERY PLAN
> -----------------------------------------------
> Finalize Aggregate
> -> Gather
> Workers Planned: 2
> -> Partial Aggregate
> -> Parallel Seq Scan on foo
> Filter: ((a % 10) = zero)
> (6 rows)
>
> select count(*) from foo where a%10 = zero;
>
> count
> -------
> 38037 -- Different random result each time, should be 100,000
> (1 row)
>
> Thoughts?
>

This issue should be fixed in attached patch (and more others).

The code is more cleaner now, there are more tests, and documentation is
mostly complete. I am sorry - my English is not good.
New features:

o ON COMMIT DROP and ON TRANSACTION END RESET -- remove temp variable on
commit, reset variable on transaction end (commit, rollback)
o LET var = DEFAULT -- reset specified variable

Regards

Pavel

> Regards,
> Dean
>