On 3/21/20 10:25 AM, Alastair McKinley wrote:
Hi all,
I have a long running query that I have tweaked along with config (e.g.
min_parallel_table_scan_size) to execute nicely and very fast in
parallel which works as expected executed directly from psql client.
The query is then embedded in a psql function like "return query select
* from function_that_executes_the_query()".
Postgres version?
What is happening in function_that_executes_the_query()?
You might want to take a look at below to see any of the conditions apply:
https://www.postgresql.org/docs/12/when-can-parallel-query-be-used.html
I am checking the explain output (using execute explain $query) just
before executing inside my function and it the plan is identical to what
I would expect, planning 8 workers. However, this query actually only
uses 1 worker and takes many times longer than when ran directly on the
psql command line with the same server configuration parameters.
Why would the explain output be different from the executed plan? Is
this a limitation of plpgsql functions? Is there any way to debug this
further?
If it is meaningful during parallel execution I notice lots of
"postgres: parallel worker" proceses in top and when executing from my
function just a single "postgres: $user $db $host($pid) SELECT" processes.
Best regards,
Alastair
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
