RE: Logical replication timeout problem

On Wed, Feb 22, 2022 at 4:56 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
Thanks for your review.

> On Tue, Feb 22, 2022 at 9:17 AM wangw.fnst@fujitsu.com
> <wangw.fnst@fujitsu.com> wrote:
> >
> > On Fri, Feb 18, 2022 at 10:51 AM Ajin Cherian <itsajin@gmail.com> wrote:
> > > Some comments:
> > Thanks for your review.
> >
> > >  I see you only track skipped Inserts/Updates and Deletes. What about
> > > DDL operations that are skipped, what about truncate.
> > > What about changes made to unpublished tables? I wonder if you could
> > > create a test script that only did DDL operations
> > > and truncates, would this timeout happen?
> > According to your suggestion, I tested with DDL and truncate.
> > While testing, I ran only 20,000 DDLs and 10,000 truncations in one
> > transaction.
> > If I set wal_sender_timeout and wal_receiver_timeout to 30s, it will time out.
> > And if I use the default values, it will not time out.
> > IMHO there should not be long transactions that only contain DDL and
> > truncation. I'm not quite sure, do we need to handle this kind of use case?
> >
> 
> I think it is better to handle such cases as well and changes related
> to unpublished tables as well. BTW, it seems Kuroda-San has also given
> some comments [1] which I am not sure are addressed.
Add handling of related use cases.

> I think instead of keeping the skipping threshold w.r.t
> wal_sender_timeout, we can use some conservative number like 10000 or
> so which we are sure won't impact performance and won't lead to
> timeouts.
Yes, it would be better. Set the threshold conservatively to 10000.

> *
> + /*
> + * skipped_changes_count is reset when processing changes that do not need
> to
> + * be skipped.
> + */
> + skipped_changes_count = 0
> 
> When the skipped_changes_count is reset, the sendTime should also be
> reset. Can we reset it whenever the UpdateProgress function is called
> with send_keep_alive as false?
Fixed.

Attached a new patch that addresses following improvements I have got so far as
comments:
1. Consider other changes that need to be skipped(truncate, DDL and function
calls pg_logical_emit_message). [suggestion by Ajin, Amit]
(Add a new function SendKeepaliveIfNecessary for trying to send keepalive message.)
2. Set the threshold conservatively to a static value of 10000.[suggestion by Amit, Kuroda-San]
3. Reset sendTime in function WalSndUpdateProgress when send_keep_alive is
false. [suggestion by Amit]

Regards,
Wang wei