release-25.2: changefeedccl: fix race advancing frontier in schemafeed #149351
+18
−2
Conversation
This file contains hidden or 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
In the schema feed, when in `updateTableHistory`, we check that the current frontier is less than the current time. However, since we release the mutex protecting frontier while validating table descriptors, it's possible for another routine to advance the frontier before the first routine tries to advance it. For example, another routine may call pauseOrResumePolling and pause polling at the same time it advances the frontier. As a consequence, it's possible for the first routine to assert fail due to the current frontier being greater than the current time when it tries to advance it. This change fixes this race by checking that the frontier is greater than the current time (endTS) again before trying to advance the frontier. If the frontier is less than or equal to the current time, the frontier does not need to be advanced and it returns. It's worth keeping the original check in, since it avoids the need to validate descriptors, and releasing the mutex also prevents the routine from holding it while validating. Epic: none Fixes: cockroachdb#148963 Release note (bug fix): Fixes a race condition when advancing a changefeed aggregator's frontier. When hit, the race condition could result in an internal error that would shut down the kvfeed and cause the changefeed to retry.
blathers-crl
bot
added
the
blathers-backport
![blathers[crl]](https://avatars.githubusercontent.com/in/59700?s=40&u=95b789b1d594ac6b74f377aa7555d8d98d63240d&v=4){kind=avatar}
|
Thanks for opening a backport. Before merging, please confirm that the change does not break backwards compatibility and otherwise complies with the backport policy. Include a brief release justification in the PR description explaining why the backport is appropriate. All backports must be reviewed by the TL for the owning area. While the stricter LTS policy does not yet apply, please exercise judgment and consider gating non-critical changes behind a disabled-by-default feature flag when appropriate. |
blathers-crl
bot
added
the
backport
|
It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR? 🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf. |
|
This change is |
andyyang890
approved these changes
Jul 1, 2025
asg0451
approved these changes
Jul 1, 2025
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.
Backport 1/1 commits from #149119 on behalf of @rharding6373.
In the schema feed, when in
updateTableHistory, we check that the current frontier is less than the current time. However, since we release the mutex protecting frontier while validating table descriptors, it's possible for another routine to advance the frontier before the first routine tries to advance it. For example, another routine may call pauseOrResumePolling and pause polling at the same time it advances the frontier.As a consequence, it's possible for the first routine to assert fail due to the current frontier being greater than the current time when it tries to advance it.This change fixes this race by checking that the frontier is greater than the current time (endTS) again before trying to advance the frontier. If the frontier is less than or equal to the current time, the frontier does not need to be advanced and it returns. It's worth keeping the original check in, since it avoids the need to validate descriptors, and releasing the mutex also prevents the routine from holding it while validating.
Epic: none
Fixes: #148963
Release note (bug fix): Fixes a race condition when advancing a changefeed aggregator's frontier. When hit, the race condition could result in an internal error that would shut down the kvfeed and cause the changefeed to retry.
Release justification: Fixes a race condition. Change is protected by a flag, defaulted on, as an escape hatch. It's ok for the flag to be defaulted on since the fix itself is simple (<5 LOC) and easy to reason about.