Re: Bypassing cursors in postgres_fdw to enable parallel plans

Rafia Sabih <rafia(dot)pghackers(at)gmail(dot)com> writes:

Hi,

>
> At present, in postgres_fdw, if a query which is using a parallel plan is fired from the remote end fails to use the
> parallel plan locally because of the presence of CURSORS. Consider the following example,
...
>
> Now, to overcome this limitation, I have worked on this idea (suggested by my colleague Bernd Helmle) of bypassing the
> cursors.

Do you know why we can't use parallel plan when cursor is used? Is It
related to this code in ExecutePlan?

/*
* Set up parallel mode if appropriate.
*
* Parallel mode only supports complete execution of a plan. If we've
* already partially executed it, or if the caller asks us to exit early,
* we must force the plan to run without parallelism.
*/
if (queryDesc->already_executed || numberTuples != 0)
use_parallel_mode = false;

Actually I can't understand the comment as well and I had this
confusion for a long time.

--
Best Regards
Andy Fan