Re: Support for N synchronous standby servers - take 2

On Thu, Oct 22, 2015 at 12:47 AM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> On Tue, Oct 20, 2015 at 8:10 PM, Beena Emerson <memissemerson(at)gmail(dot)com> wrote:
>>
>> On Mon, Oct 19, 2015 at 8:47 PM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>
>> wrote:
>>>
>>>
>>> Hi,
>>>
>>> Attached patch is a rough patch which supports multi sync replication
>>> by another approach I sent before.
>>>
>>> The new GUC parameters are:
>>> * synchronous_standby_num, which specifies the number of standby
>>> servers using sync rep. (default is 0)
>>> * synchronous_replication_method, which specifies replication method;
>>> priority or quorum. (default is priority)
>>>
>>> The behaviour of 'priority' and 'quorum' are same as what we've been
>>> discussing.
>>> But I write overview of these here again here.
>>>
>>> [Priority Method]
>>> The standby server has each different priority, and the active standby
>>> servers having the top N priroity are become sync standby server.
>>> If synchronous_standby_names = '*', the all active standby server
>>> would be sync standby server.
>>> If you want to set up standby like 9.5 or before, you can set
>>> synchronous_standby_num = 1.
>>>
>>
>>
>> I used the following setting with 2 servers A and D connected:
>>
>> synchronous_standby_names = 'A,B,C,D'
>> synchronous_standby_num = 2
>> synchronous_replication_method = 'priority'
>>
>> Though s_r_m = 'quorum' worked fine, changing it to 'priority' caused
>> segmentation fault.
>>
>
> Thank you for taking a look!
> This patch is a tool for discussion, so I'm not going to fix this bug
> until getting consensus.
>
> We are still under the discussion to find solution that can get consensus.
> I felt that it's difficult to select from the two approaches within
> this development cycle, and there would not be time to implement such
> big feature even if we selected.
> But this feature is obviously needed by many users.
> So I'm considering more simple and extensible something solution, the
> idea I posted is one of them.
> The another worth considering approach is that just specifying the
> number of sync standby. It also can cover the main use cases in
> some-cases.

Yes, it covers main and simple use case like "I want to have multiple
synchronous replicas!". Even if we miss quorum commit at the first
version, the feature is still very useful.

Regards,

--
Fujii Masao