Alert when RocksDB does not respect upper bound

Author: bitonic

cpp/cdc/CDCDB.cpp

@@ -1749,6 +1749,8 @@ struct CDCDBImpl {
                     LOG_DEBUG(_env, "selected %s as next in line after finishing %s", nextK().txnId(), txnId);
                     mightBeReady.emplace_back(nextK().txnId());
                     ROCKS_DB_CHECKED(dbTxn.Put(_dirsToTxnsCf, sentinelK.toSlice(), sentinelV.toSlice()));
+                } else {
+                    RAISE_ALERT_APP_TYPE(_env, XmonAppType::DAYTIME, "Unexpectedly stepped from %s to %s, is RocksDB not respecting our upper bound?", dirId, nextK().dirId());
                 }
             } else {
                 ROCKS_DB_CHECKED(it->status());