Dear Horiguchi-san,
> Thus how about before entering an apply_delay, logrep worker sending a
> kind of crafted feedback, which reports commit_data.end_lsn as
> flushpos? A little tweak is needed in send_feedback() but seems to
> work..
Thanks for replying! I tested your saying but it could not work well...
I made PoC based on the latest time-delayed patches [1] for non-streaming case.
Apply workers that are delaying applications send begin_data.final_lsn as
recvpos and flushpos in send_feedback().
Followings were contents of the feedback message I got, and we could see that
recv and flush were overwritten.
```
DEBUG: sending feedback (force 1) to recv 0/1553638, write 0/1553550, flush
0/1553638
CONTEXT: processing remote data for replication origin "pg_16390" during
message type "BEGIN" in transaction 730, finished at 0/1553638
```
In terms of walsender, however, sentPtr seemed to be slightly larger than
flushed position on subscriber.
```
(gdb) p MyWalSnd->sentPtr
$2 = 22361760
(gdb) p MyWalSnd->flush
$3 = 22361656
(gdb) p *MyWalSnd
$4 = {pid = 28807, state = WALSNDSTATE_STREAMING, sentPtr = 22361760,
needreload = false, write = 22361656,
flush = 22361656, apply = 22361424, writeLag = 20020343, flushLag = 20020343,
applyLag = 20020343,
sync_standby_priority = 0, mutex = 0 '\000', latch = 0x7ff0350cbb94,
replyTime = 725113263592095}
```
Therefore I could not shut down the publisher node when applications were
delaying.
Do you have any opinions about them?
```
$ pg_ctl stop -D data_pub/
waiting for server to shut
down............................................................... failed
pg_ctl: server does not shut down
```
[1]:
https://www.postgresql.org/message-id/tycpr01mb83730a3e21e921335f6efa38ed...@tycpr01mb8373.jpnprd01.prod.outlook.com
Best Regards,
Hayato Kuroda
FUJITSU LIMITED
