In a recent help ticket a customer was wondering about a large number of logs with message "TransactionCoordinator terminating with unexpected error" and "error": "TransactionCoordinatorCanceled: Transaction exceeded deadline or newer transaction started". The customer did not report any known impact but were confused about the increase in this log's volume after updating to 8.0.

On investigation I found that the vast majority of these transactions succeeded. It appears when the transaction coordinator service creates a new transaction, it cancels any previously-existing transaction on that logical session. If that transaction happened to be single-shard, it'll set that transaction coordinator's status to TransactionCoordinatorCanceled with the message above, even though the transaction completed just fine.

While it's not an SDAP impact, it would be less confusing for customers if this log line were more clear. In this case, we could probably track on the TransactionCoordinator that the transaction committed, even if it did not call _reserveKickOffCommitPromise() in the process.