Re: Parallel query execution with SPI

On Fri, Mar 31, 2017 at 3:33 AM, Konstantin Knizhnik
<k(dot)knizhnik(at)postgrespro(dot)ru> wrote:
> It is possible to execute query concurrently using SPI?
> If so, how it can be enforced?
> I tried to open cursor with CURSOR_OPT_PARALLEL_OK flag but it doesn't help:
> query is executed by single backend while the same query been launched at
> top level uses parallel plan:
>
> fsstate->portal = SPI_cursor_open_with_args(NULL, fsstate->query,
> fsstate->numParams, argtypes, values, nulls, true, CURSOR_OPT_PARALLEL_OK);
> ...
> SPI_cursor_fetch(fsstate->portal, true, 1);

Parallel execution isn't possible if you are using a cursor-type
interface, because a parallel query can't be suspended and resumed
like a non-parallel query. If you use a function that executes the
query to completion in one go, like SPI_execute_plan, then it's cool.
See also commit 61c2e1a95f94bb904953a6281ce17a18ac38ee6d.

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Robert Haas
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