release-25.3: changefeedccl: fix race advancing frontier in schemafeed #149352
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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.
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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.