Am 12.08.2022 um 21:02 schrieb Rick Otten:



On Fri, Aug 12, 2022 at 2:50 PM Nico Heller <nico.hel...@posteo.de> wrote:

    Good day,

    consider the following query:

    WITH aggregation(
         SELECT
                a.*,
               (SELECT array_agg(b.*) FROM b WHERE b.a_id = a.id
    <http://a.id>) as "bs",
               (SELECT array_agg(c.*) FROM c WHERE c.a_id = a.id
    <http://a.id>) as "cs",
               (SELECT array_agg(d.*) FROM d WHERE d.a_id = a.id
    <http://a.id>) as "ds",
               (SELECT array_agg(e.*) FROM d WHERE e.a_id = a.id
    <http://a.id>) as "es"
         FROM a WHERE a.id <http://a.id> IN (<some big list, ranging
    from 20-180 entries)
    )
    SELECT to_jsonb(aggregation.*) as "value" FROM aggregation;


- You do have an index on `b.a_id` and `c.a_id`, etc... ?  You didn't say...
Yes there are indices on all referenced columns of the subselect (they are all primary keys anyway)
- Are you sure it is the `to_jsonb` that is making this query slow?
Yes, EXPLAIN ANALYZE shows a doubling of execution time - I don't have numbers on the memory usage difference though

- Since you are serializing this for easy machine readable consumption outside of the database, does it make a difference if you use `to_json` instead?

Using to_json vs. to_jsonb makes no difference in regards to runtime, I will check if the memory consumption is different on monday - thank you for the idea!

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