I have been working with pg_stat_statements extension to PG and it give us a way to see the actual SQL statements being executed by lemmy_server and the number of times they are being called.
This has less overhead than cranking up logging and several cloud computing services enable it by default (example) - so I don’t believe it will have a significant slow down of the server.
A DATABASE RESTART WILL BE REQUIRED
It does require that PostgreSQL be restarted. Which can take 10 or 15 seconds, typically.
Debian / Ubuntu install steps
https://pganalyze.com/docs/install/self_managed/02_enable_pg_stat_statements_deb
Following the conventions of “Lemmy from Scratch” server install commands:
sudo -iu postgres psql -c "ALTER SYSTEM SET shared_preload_libraries = 'pg_stat_statements';"
Followed by a restart of the PostgreSQL service.
Update July 24, 2023
Some major stored procedure SQL problems were overlooked until 2 days ago. I submitted revised statements to fix a massive write operation on every single post and comment creation on a local site. The site_aggregates table… every row modified instead of a single row. https://github.com/LemmyNet/lemmy/pull/3704
I was curious why pg_stat_statements didn’t draw more attention to the INSERT statements hitting so many rows, and I found out that by default it does not take into account stored procedure execution! https://stackoverflow.com/questions/56741860/pg-stat-activity-how-to-see-current-activity-inside-a-running-stored-procedure
pg_stat_statements.track = allNow I’m seeing far more activity than I have been looking at for the past 2 months… the stored procedure statements are showing up!
Install steps: https://gist.github.com/rcanepa/535163dc249539912c25
@[email protected] If you find queries that are slow could you post the EXPLAIN ANALYZE here or send them to me? You can do it manually or maybe use https://www.postgresql.org/docs/current/auto-explain.html
