TestEngineering/Performance/FAQ: Difference between revisions

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 A final note, Mozilla-Beta is a branch where little development takes place.  The volume is really low and alerts come 5 days (or more) later.  It is important to address Mozilla-Beta alerts ASAP because that is what we are shipping to customers.
+=== What is coalescing ===
+Coalescing is a term we use for when we schedule jobs to run on a given machine.  When the load is high these jobs are placed in a queue and the longer the queue we skip over some of the jobs.  This allows us to get results on more recent changesets faster.
+This affects talos numbers as we see regressions which show up over >1 changeset that is pushed.  We have to manually fill in the coalesced jobs (including builds sometimes) to ensure we have the right changeset to blame for the regression.
+Some things to be aware of:
+* missing test jobs - This could be as easy as waiting for jobs to finish, or scheduling the missing job assuming it was coalesced, otherwise, it could be a missing build.
+* missing builds -  we would have to generate builds, which automatically schedules test jobs, sometimes these test jobs are coalesced and not run.
+* results might not be possible due to build failures, or test failures
+* [[TestEngineering/Performance/Sheriffing/Tree_FAQ#What_is_PGO|pgo builds]] are not coalesced, they just run much less frequently.  Most likely a pgo build isn't the root cause
+Here is a view on treeherder of missing data (usually coalescing):
+[[File:Coalescing_markedup.png]]
+Note the two pushes that have no data (circled in red).  If the regression happened around here, we might want to backfill those two jobs so we can ensure we are looking at the push which caused the regression instead of >1 push.
 ==Alert==