[JDBC] JDBC: logical replication and LSN feedback

Hi,

This is a follow-up from my previous question

(https://www.postgresql.org/message-id/trinity-903b9111-dde7-4901-8130-86924336c456-1505912478894%403c-app-mailcom-bs15).

I created a git to guide my question, see
https://github.com/yasontr/pg-jdbc-logical-decoding.

Please follow the install steps on this page. After this, you can run
the application with Maven. This application listens to a replication
slot. See
https://github.com/yasontr/pg-jdbc-logical-decoding/blob/master/src/main/java/yasontr/pg_jdbc_logical_decoding/Main.java
for the code of the application.

The problem I am seeing can be reproduced as following:

1) start the application
2) insert a dummy row to the test table: insert into test(key, value)
values (1, 'test');
3) now you see in the console:

event:
{"change":[{"kind":"insert","schema":"public","table":"test","columnnames":["key","value"],"columntypes":["int4","text"],"columnvalues":[1,"test"]}]}
last received LSN: LSN{1A/AD2EEB0}

4) close the application
5) start the application again
6) now you see again the same event again in the console:

event:
{"change":[{"kind":"insert","schema":"public","table":"test","columnnames":["key","value"],"columntypes":["int4","text"],"columnvalues":[1,"test"]}]}
last received LSN: LSN{1A/AD2EEB0}

As you can see in the code, I am confirming the event with its LSN:
   stream.setAppliedLSN(stream.getLastReceiveLSN());   stream.setFlushedLSN(stream.getLastReceiveLSN());
stream.forceUpdateStatus();

So I would expect that the event is marked, possibly removed from the
WAL and that it would not be resent to the consumer(s).

Could anyone explain why this is happening?

As a side-question, what is the difference between setAppliedLSN and
setFlushedLSN and why/when do I need both/just one? The javadocs are
not really helpful here.

Thanks and best regards,

Yason TR


-- 
Sent via pgsql-jdbc mailing list (pgsql-jdbc@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-jdbc