There is an ordering issue with graceful shutdown on Postgres databases using Embedded engine. The replication stream is closed before flush.

The following things happen when EmbeddedEngine.close() is called:

1. The PostgresStreamingChangeEventSource.execute(..) method is terminated and the following finally block is triggered.
   See LOC https://github.com/debezium/debezium/blob/master/debezium-connector-postgres/src/main/java/io/debezium/connector/postgresql/PostgresStreamingChangeEventSource.java#L152-L173

   public void execute(ChangeEventSourceContext context) throws InterruptedException {
     ...
           finally {
               if (replicationConnection != null) {
                  ...
                  replicationStream.set(null);
               }
       }
   }
   

2. In EmbeddedEngine the finally block of the run method is invoked and this code block is executed:
   See LOC:  https://github.com/debezium/debezium/blob/86cb71ad8b063a66fff8148a9a2dc94830d21d09/debezium-embedded/src/main/java/io/debezium/embedded/EmbeddedEngine.java#L838-L850

                       finally {
                               ...
                               // Always commit offsets that were captured from the source records we actually processed ...
                               commitOffsets(offsetWriter, commitTimeout, task);
                               ...
                           }
   

3. This triggers the execution of the PostgresStreamingChangeEventSource commitOffset method, but replicationStream was set to null in step 1, so the flushLsn never happens:
   See LOC: https://github.com/debezium/debezium/blob/master/debezium-connector-postgres/src/main/java/io/debezium/connector/postgresql/PostgresStreamingChangeEventSource.java#L334-L347

       @Override
       public void commitOffset(Map<String, ?> offset) {
           try {
               ...
               if (replicationStream != null && lsn != null) {
                  ...
                   // tell the server the point up to which we've processed data, so it can be free to recycle WAL segments
                   replicationStream.flushLsn(lsn);
               }
               ...
       }
   

4. The shutdown sequence completes with no exceptions raised, despite the complete failure to flush LSNs