RE: [PATCH] Reuse Workers and Replication Slots during Logical Replication

Dear Melih,

> Thanks for the 0003 patch. But it did not work for me. Can you create
> a subscription successfully with patch 0003 applied?
> I get the following error: " ERROR:  table copy could not start
> transaction on publisher: another command is already in progress".

You got the ERROR when all the patches (0001-0005) were applied, right?
I have focused on 0001 and 0002 only, so I missed something.
If it was not correct, please attach the logfile and test script what you did.

As you might know, the error is output when the worker executs walrcv_endstreaming()
before doing walrcv_startstreaming().

> I think streaming needs to be ended before moving to another table. So
> I changed the patch a little bit

Your modification seemed not correct. I applied only first three patches (0001-0003), and
executed attached script. Then I got following error on subscriber (attached as N2.log):

> ERROR:  could not send end-of-streaming message to primary: no COPY in progress

IIUC the tablesync worker has been already stopped streaming without your modification.
Please see process_syncing_tables_for_sync():

```
    if (MyLogicalRepWorker->relstate == SUBREL_STATE_CATCHUP &&
        current_lsn >= MyLogicalRepWorker->relstate_lsn)
    {
        TimeLineID    tli;
        char        syncslotname[NAMEDATALEN] = {0};
        char        originname[NAMEDATALEN] = {0};

        MyLogicalRepWorker->relstate = SUBREL_STATE_SYNCDONE;
...
        /*
         * End streaming so that LogRepWorkerWalRcvConn can be used to drop
         * the slot.
         */
        walrcv_endstreaming(LogRepWorkerWalRcvConn, &tli);
```

This means that following changes should not be in the 0003, should be at 0005.
PSA fixed patches.

```
+    /*
+     * If it's already connected to the publisher, end streaming before using
+     * the same connection for another iteration
+     */
+    if (LogRepWorkerWalRcvConn != NULL)
+    {
+        TimeLineID tli;
+        walrcv_endstreaming(LogRepWorkerWalRcvConn, &tli);
+    }
```


Besides, cfbot could not apply your patch set [1]. According to the log, the
bot tried to apply 0004 and 0005 first and got error. IIUC you should assign
same version number within the same mail, like v16-0001, v16-0002,....

[1]: http://cfbot.cputube.org/patch_43_3784.log

Best Regards,
Hayato Kuroda
FUJITSU LIMITED