From: | "Hayato Kuroda (Fujitsu)" <kuroda(dot)hayato(at)fujitsu(dot)com> |
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To: | 'Ajin Cherian' <itsajin(at)gmail(dot)com> |
Cc: | shveta malik <shveta(dot)malik(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Peter Smith <smithpb2250(at)gmail(dot)com>, "Drouvot, Bertrand" <bertranddrouvot(dot)pg(at)gmail(dot)com>, Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>, Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
Subject: | RE: Synchronizing slots from primary to standby |
Date: | 2023-10-31 01:46:09 |
Message-ID: | TYAPR01MB5866C7FB1A2C26D9F1DF8E11F5A0A@TYAPR01MB5866.jpnprd01.prod.outlook.com |
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Lists: | pgsql-hackers |
Dear Ajin,
Thanks for your reply!
> On Thu, Oct 26, 2023 at 6:08 PM Hayato Kuroda (Fujitsu)
> <kuroda(dot)hayato(at)fujitsu(dot)com> wrote:
> >
> > Dear Shveta,
> >
> > > PFA v25 patch set. The changes are:
> >
> > Thanks for making the patch! It seems that there are lots of comments, so
> > I can put some high-level comments for 0001.
> > Sorry if there are duplicated comments.
> >
> > 1.
> > The patch seemed not to consider the case that failover option between
> replication
> > slot and subscription were different. Currently slot option will be overwritten
> > by subscription one.
> >
> > Actually, I'm not sure what specification is better. Regarding the two_phase,
> > 2PC will be decoded only when the both of settings are true. Should we follow?
> >
>
> But this is the intention, we want the Alter subscription to be able
> to change the failover behaviour
> of the slot.
I had not understood how two_phase is enabled. I found that slot->data.two_phase
is overwritten in CreateDecodingContext(), so the failover option now follows two_phase, right?
(I think the overwritten of data.failover should be also done at CreateDecodingContext()).
> > 2.
> > Currently ctx->failover is set only in the pgoutput_startup(), but not sure it is
> OK.
> > Can we change the parameter in CreateDecodingContext() or similar functions?
> >
> > Because IIUC it means that only slots which have pgoutput can wait. Other
> > output plugins must understand the change and set faliover flag as well -
> > I felt it is not good. E.g., you might miss to enable the parameter in
> test_decoding.
> >
> > Regarding the two_phase parameter, setting on plugin layer is good because it
> > quite affects the output. As for the failover, it is not related with the
> > content so that all of slots should be enabled.
> >
> > I think CreateDecodingContext or StartupDecodingContext() is the common
> path.
> > Or, is it the out-of-scope for now?
>
> Currently, the failover field is part of the options list in the
> StartReplicationCmd. This gives some
> level of flexibility such that only plugins that are interested in
> this need to handle it. The options list
> is only deparsed by plugins. If we move it to outside of the options list,
> this sort of changes the protocol for START_REPLICATION and will
> impact all plugins.
> But I agree to your larger point that, we need to do it in such a way that
> other plugins do not unintentionally change the 'failover' behaviour
> of the originally created slot.
> Maybe I can code it in such a way that, only if the failover option is
> specified in the list of options
> passed as part of START_REPLICATION will it change the original slot
> created 'failover' flag by adding
> another flag "failover_opt_given". Plugins that set this, will be able
> to change the failover flag of the slot,
> while plugins that do not support this will not set this and the
> failover flag of the created slot will remain.
> What do you think?
May be OK, but I came up with a corner case that external plugins have a streaming
option 'failover'. What should be? Has the option been reserved?
Best Regards,
Hayato Kuroda
FUJITSU LIMITED
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