Re: Bypassing cursors in postgres_fdw to enable parallel plans

On Fri, Jan 17, 2025 at 7:03 AM Rafia Sabih <rafia(dot)pghackers(at)gmail(dot)com> wrote:
> Indeed you are right.
> Firstly, accept my apologies for not mentioning you in credits for this work. Thanks a lot for your efforts, discussions with you were helpful in shaping this patch and bringing it to this level.
>
> Next, yes the last version was using tuplestore for queries within the same transaction after the second query. To overcome this, I came across this method to identify if there is any other simultaneous query running with the current query; now there is an int variable num_queries which is incremented at every call of postgresBeginForeignScan and decremented at every call of postgresEndForeignScan. This way, if there are simultaneous queries running we get the value of num_queries greater than 1. Now, we check the value of num_queries and use tuplestore only when num_queries is greater than 1. So, basically the understanding here is that if postgresBeginForeignScan is called and before the call of postgresEndForeignScan if another call to postgresBeginForeignScan is made, then these are simultaneous queries.

This wouldn't be true in case of error, I believe.

--
Robert Haas
EDB: http://www.enterprisedb.com