One of the best things about performance monitoring is that it sometimes shows up problems in very unexpected areas. Yesterday while working on some improvements to telemetry, I noticed that the telemetry packets being sent had information for slowSQLStartup. That is, there were some SQL queries (4 of them, to be exact; 3 unique queries) that were taking more than 150 ms to run just during xpcshell testing.
These queries were run by the addons manager and already have a bug on file.
I’m guessing that this slow SQL does not occur during all xpcshell tests, but only those that create a profile (about 5% of tests). which would translate into ~1% of xpcshell testing time. Still, speedups are speedups, and fixing these queries would be a good speedup for Firefox users generally.