mvcc: avoid negative watcher count metrics #11882
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
The watch count metrics are not robust to duplicate cancellations. These cause the count to be decremented twice, leading eventually to negative counts. We are seeing this in production. The duplicate cancellations themselves are not themselves a big problem (except performance), but they are caused by the new proactive cancellation logic (etcd-io#11850) which cancels proactively even immediately before initiating a Close, thus nearly guaranteeing a Close-cancel race, as discussed in watchable_store.go. We can avoid this in most cases by not sending a cancellation when we are going to Close.
jackkleeman
force-pushed
the
dup-cancel-metrics
branch
from
08b078f to
c0a2e09
Compare
|
cc @gyuho |
|
lgtm |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
The watch count metrics are not robust to duplicate cancellations. These
cause the count to be decremented twice, leading eventually to negative
counts. We are seeing this in production. The duplicate cancellations
themselves are not themselves a big problem (except performance), but
they are caused by the new proactive cancellation logic (#11850) which
cancels proactively even immediately before initiating a Close, thus
nearly guaranteeing a Close-cancel race, as discussed in
watchable_store.go. We can avoid this in most cases by not sending a
cancellation when we are going to Close.
The client change is simply for the benefit of those using the 3.5 client against an old cluster - we could remove it if desired. The metrics fix on the server side is sufficient, and that's the real bug here arguably.