How lemmy.ca took on finding why PostgreSQL was at 100% CPU and crashing the Lemmy website this past weekend. PostgreSQL auto_explain

IIRC, it was lemmy.ca full copy of live data that was used (copy made on development system, not live server - if I'm following). Shared Saturday July 22 on GitHub was this procedure:

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Notable is the AUTO_EXPLAIN SQL activation statements:

LOAD 'auto_explain';
SET auto_explain.log_min_duration = 0;
SET auto_explain.log_analyze = true;
SET auto_explain.log_nested_statements = true;

This technique would be of great use for developers doing changes and study of PostgreSQL activity. Thank you!

3 comments

Yeah this was the only way I could get visibility into the queries running inside the triggers.
- Thank you for sharing, I had not come across the auto_explain technique and was manually pulling out SQL from pg_stat_statements and trying to match up to runtime parameters for $1 $2 etc with EXPLAIN
  
  Oof yeah, that's not gonna be a fun way to troubleshoot!
  
  Thanks for taking the ball and running with this, looks like it's getting a lot of attention now and hopefully next release will have some juicy sql improvements!