The PostingsForMatchersCache has a comment that says:
// FIXME: do we need to cancel the call to postingsForMatchers if all the callers waiting for the result have
// cancelled their context?
During the weekend we learned the hard way that, yes, we should. The reason is that the underlying PostingsForMatchers() honor context cancellation, but when it's called through the single flight promise used by the cache, we run it with a new context.Background() and so it never gets canceled.
If the execution of the underlying PostingsForMatchers() takes a very long time (e.g. due to an insanely complex regexp), then it's undesirable keep it running if the request has been canceled. We prefer to cancel the PostingsForMatchers() execution.
The
PostingsForMatchersCachehas a comment that says:During the weekend we learned the hard way that, yes, we should. The reason is that the underlying
PostingsForMatchers()honor context cancellation, but when it's called through the single flight promise used by the cache, we run it with a newcontext.Background()and so it never gets canceled.If the execution of the underlying
PostingsForMatchers()takes a very long time (e.g. due to an insanely complex regexp), then it's undesirable keep it running if the request has been canceled. We prefer to cancel thePostingsForMatchers()execution.This PR addresses it.