Re: Logical replication and synchronous replication

On Tue, Apr 18, 2017 at 9:05 PM, Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:
> On 18 April 2017 at 18:55, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>> Hi,
>>
>> As doc of logical decoding said as a note[1], logical replication can
>> support the synchronous replication with some restriction. But In
>> addition to this, IIUC in logical replication decoded data is sent to
>> subscribers only when the commit WAL record is decoded (calls
>> ReorderBufferCommit) .
>
> Correct.
>
>> It means that the local SQL execution and
>> applying the decoded data on subscriber side are always executed in a
>> sequential order, and the response time can simply be doubled or even
>> more (OTOH a good point is that decoded data of aborted transaction is
>> never sent to subscriber). I think there will be a lot of peoples who
>> want to use logical synchronous replication but this is a big
>> restriction for such user. I think we should document it or deal with
>> it.
>> Thought?
>
> Definitely should be documented. I think it's covered under logical
> decoding, but needs at least an xref.

Yes, I think so too. I'll send a patch for that this week, and maybe
will propose a improvement patch for logical sync replication in the
next release cycle.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center