Re: Force streaming every change in logical decoding

On Sat, Dec 10, 2022 at 5:03 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Tue, Dec 6, 2022 at 11:53 AM shiy(dot)fnst(at)fujitsu(dot)com
> <shiy(dot)fnst(at)fujitsu(dot)com> wrote:
> >
> > Hi hackers,
> >
> > In logical decoding, when logical_decoding_work_mem is exceeded, the changes are
> > sent to output plugin in streaming mode. But there is a restriction that the
> > minimum value of logical_decoding_work_mem is 64kB. I tried to add a GUC to
> > allow sending every change to output plugin without waiting until
> > logical_decoding_work_mem is exceeded.
> >
> > This helps to test streaming mode. For example, to test "Avoid streaming the
> > transaction which are skipped" [1], it needs many XLOG_XACT_INVALIDATIONS
> > messages. With the new option, it can be tested with fewer changes and in less
> > time. Also, this new option helps to test more scenarios for "Perform streaming
> > logical transactions by background workers" [2].
>
> Some comments on the patch
>
...
> This GUC name "force_stream_mode" somehow appears like we are forcing
> this streaming mode irrespective of whether the
> subscriber has requested for this mode or not. But actually it is not
> that, it is just streaming each change if
> it is enabled. So we might need to think on the name (at least we
> should avoid using *mode* in the name IMHO).
>

I thought the same. Names like those shown below might be more appropriate:
stream_checks_work_mem = true/false
stream_mode_checks_size = true/false
stream_for_large_tx_only = true/false
... etc.

The GUC name length could get a bit unwieldy but isn't it better for
it to have the correct meaning than to have a shorter but slightly
ambiguous name? Anyway, it is a developer option so I guess longer
names are less of a problem.

------
Kind Regards,
Peter Smith.
Fujitsu Australia