3. Replicate published sequences via walsender at the time of shutdown or incrementally while decoding checkpoint record. The two ways to achieve this are: (a) WAL log a special NOOP record just before shutting down checkpointer. Then allow the WALsender to read the sequence data and send it to the subscriber while decoding the new NOOP record. (b) Similar to the previous idea but instead of WAL logging a new record directly invokes a decoding callback after walsender receives a request to shutdown which will allow pgoutput to read and send required sequences. This approach has a drawback that we are adding more work at the time of shutdown but note that we already waits for all the WAL records to be decoded and sent before shutting down the walsender during shutdown of the node.
Any other ideas?
In case of primary crash the sequence won't get replicated. That is true even with the previous approach in case walsender is shut down because of a crash, but it is more serious with this approach. How about periodically sending this information?