Re: logical decoding of two-phase transactions

> On 20 Mar 2017, at 16:39, Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:
>
> On 20 March 2017 at 20:57, Stas Kelvich <s(dot)kelvich(at)postgrespro(dot)ru> wrote:
>>
>>> On 20 Mar 2017, at 15:17, Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:
>>>
>>>> I thought about having special field (or reusing one of the existing fields)
>>>> in snapshot struct to force filtering xmax > snap->xmax or xmin = snap->xmin
>>>> as Petr suggested. Then this logic can reside in ReorderBufferCommit().
>>>> However this is not solving problem with catcache, so I'm looking into it right now.
>>>
>>> OK, so this is only an issue if we have xacts that change the schema
>>> of tables and also insert/update/delete to their heaps. Right?
>>>
>>> So, given that this is CF3 for Pg10, should we take a step back and
>>> impose the limitation that we can decode 2PC with schema changes or
>>> data row changes, but not both?
>>
>> Yep, time is tight. I’ll try today/tomorrow to proceed with this two scan approach.
>> If I’ll fail to do that during this time then I’ll just update this patch to decode
>> only non-ddl 2pc transactions as you suggested.
>
> I wasn't suggesting not decoding them, but giving the plugin the
> option of whether to proceed with decoding or not.
>
> As Simon said, have a pre-decode-prepared callback that lets the
> plugin get a lock on the 2pc xact if it wants, or say it doesn't want
> to decode it until it commits.
>
> That'd be useful anyway, so we can filter and only do decoding at
> prepare transaction time of xacts the downstream wants to know about
> before they commit.

Ah, got that. Okay.

> --
> Craig Ringer http://www.2ndQuadrant.com/
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