mirror of
https://github.com/github/rails.git
synced 2026-04-26 03:00:59 -04:00
cfeac38e2b
This commit vastly reduces the impact of auto explain logging when enabled, while keeping a negligible cost when disabled. The first implementation was based on the idea of subscribing to "sql.active_record" when needed, and unsubscribing once done. This is the idea behind AR::Relation#explain. Subscribe, collect, unsubscribe. But with the current implementation of notifications unsubscribing is costly, because it wipes an internal cache and that puts a penalty on the next event. So we are switching to an approach where a long-running subscriber is listening. Instead of collecting the queries with a closure in a dedicated subscriber, now we setup a thread local. If the feature is disabled by setting the threshold to nil, the subscriber will call a method that does nothing. That's totally cheap.