Re: PATCH: logical_work_mem and logical streaming of large in-progress transactions

On Sun, Jul 5, 2020 at 8:37 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Tue, Jun 30, 2020 at 10:13 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> >
> >
> > Yeah, I have run the regression suite, I can see a lot of failure
> > maybe we can somehow see the diff and confirm that all the failures
> > are due to rollback to savepoint only. I will work on this.
>
> I have compared the changes logged at command end vs logged at commit
> time. I have ignored the invalidation for the transaction which has
> any aborted subtransaction in it. While testing this I found one
> issue, the issue is that if there are some invalidation generated
> between last command counter increment and the commit transaction then
> those were not logged. I have fixed the issue by logging the pending
> invalidation in RecordTransactionCommit. I will include the changes
> in the next patch set.
>

I think it would have been better if you could have given examples for
such cases where you need this extra logging. Anyway, below are few
minor comments on this patch:

1.
+ /*
+ * Log any pending invalidations which are adding between the last
+ * command counter increment and the commit.
+ */
+ if (XLogLogicalInfoActive())
+ LogLogicalInvalidations();

I think we can change this comment slightly and extend a bit to say
for which kind of special cases we are adding this. "Log any pending
invalidations which are added between the last CommandCounterIncrement
and the commit. Normally for DDLs, we log this at each command end,
however for certain cases where we directly update the system table
the invalidations were not logged at command end."

Something like above based on cases that are not covered by command
end WAL logging.

2.
+ * Emit WAL for invalidations. This is currently only used for logging
+ * invalidations at the command end.
+ */
+void
+LogLogicalInvalidations()

After this is getting used at a new place, it is better to modify the
above comment to something like: "Emit WAL for invalidations. This is
currently only used for logging invalidations at the command end or at
commit time if any invalidations are pending."

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com