Re: Perform streaming logical transactions by background workers and parallel apply

On Wed, Jan 4, 2023 at 4:25 PM houzj(dot)fnst(at)fujitsu(dot)com
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>

> Attach the new patch set.
> Apart from addressing Sawada-San's comments, I also did some other minor
> changes in the patch:

I have done a high-level review of 0001, and later I will do a
detailed review of this while reading through the patch I think some
of the comments need some changes..

1.
+ The deadlock can happen in
+ * the following ways:
+ *

+ * 4) Lock types
+ *
+ * Both the stream lock and the transaction lock mentioned above are
+ * session-level locks because both locks could be acquired outside the
+ * transaction, and the stream lock in the leader needs to persist across
+ * transaction boundaries i.e. until the end of the streaming transaction.

I think the Lock types should not be listed with the number 4).
Because point number 1,2 and 3 are explaining the way how deadlocks
can happen but 4) doesn't fall under that category.

2.
+ * Since the database structure (schema of subscription tables, constraints,
+ * etc.) of the publisher and subscriber could be different, applying
+ * transactions in parallel mode on the subscriber side can cause some
+ * deadlocks that do not occur on the publisher side.

I think this paragraph needs to be rephrased a bit. It is saying that
some deadlock can occur on subscribers which did not occur on the
publisher. I think what it should be conveying is that the deadlock
can occur due to concurrently applying the conflicting/dependent
transactions which are not conflicting/dependent on the publisher due
to <explain reason>. Because if we create the same schema on the
publisher it might not have ended up in a deadlock instead it would
have been executed in sequence (due to lock waiting). So the main
point we are conveying is that the transaction which was independent
of each other on the publisher could be dependent on the subscriber
and they can end up in deadlock due to parallel apply.

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com