Subject: Re: Linear slow-down while inserting into a table with an ON INSERT
 trigger ?
To: David Rowley <dgrowleyml@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>
Cc: pgsql-performance <pgsql-performance@postgresql.org>
References: <62070f97-13e7-df73-bed1-f8e48c12bf2d@code-sourcery.de>
 <20210717044026.GA19498@telsasoft.com>
 <CAApHDvr-kFAmOihG1FxVZfgdV_e5TR8cU3n+QPkYwJ8XqmA4YQ@mail.gmail.com>
From: Tobias Gierke <tobias.gierke@code-sourcery.de>
Message-ID: <9f2df5fb-50a4-fefd-810a-d3b915717190@code-sourcery.de>
Date: Sun, 18 Jul 2021 09:25:19 +0200
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Great idea ! This brought the time per INSERT into the parent table down 
to a consistent ~0.065ms again (compared to 0.05ms when completely 
removing the trigger, so penalty for the trigger is roughly ~20%).

> On Sat, 17 Jul 2021 at 16:40, Justin Pryzby <pryzby@telsasoft.com> wrote:
>> You could run a single UPDATE rather than 30k triggers.
>> Or switch to an INSERT on the table, with an index on it, and call
>> max(last_parent_table_change) from whatever needs to ingest it.  And prune the
>> old entries and vacuum it outside the transaction.  Maybe someone else will
>> have a better suggestion.
> Maybe just change the UPDATE statement to:
>
> UPDATE data_sync SET last_parent_table_change=CURRENT_TIMESTAMP WHERE
> last_parent_table_change <> CURRENT_TIMESTAMP;
>
> That should reduce the number of actual updates to 1 per transaction.
>
> David