Re: possibility to define only local cursors

čt 30. 11. 2023 v 6:45 odesílatel Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
napsal:

> Hi
>
> one my customer migrated a pretty large application from Oracle, and when
> did performance tests, he found very high memory usage related probably to
> unclosed cursors. The overhead is significantly bigger than on Oracle
> (probably Oracle closes cursors after leaving cursor's variable scope, I
> don't know. Maybe it just uses a different pattern with shorter
> transactions on Oracle). He cannot use FOR cycle, because he needs to hold
> code in form that allows automatic translation from PL/SQL to PL/pgSQL for
> some years (some years he will support both platforms).
>
> DECLARE qNAJUPOSPL refcursor;
> BEGIN
> OPEN qNAJUPOSPL FOR EXECUTE mSqNAJUPOSPL;
> LOOP
> FETCH qNAJUPOSPL INTO mID_NAJVUPOSPL , mID_NAJDATSPLT , mID_PREDPIS;
> EXIT WHEN NOT FOUND; /* apply on qNAJUPOSPL */
> END LOOP;
> END;
>
> Because plpgsql and postgres can be referenced just by name then it is not
> possible to use some reference counters and close cursors when the
> reference number is zero. Can we introduce some modifier that forces
> closing the unclosed cursor before the related scope is left?
>
> Some like `DECLATE curvar refcursor LOCAL`
>
> Another way to solve this issue is just warning when the number of opened
> cursors crosses some limit. Later this warning can be disabled, increased
> or solved. But investigation of related memory issues can be easy then.
>

it can be implemented like extra warning for OPEN statement.

>
> Comments, notes?
>
> Regards
>
> Pavel
>
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