Re: Support for N synchronous standby servers - take 2

On Thu, Jun 25, 2015 at 7:32 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> On 25 June 2015 at 05:01, Michael Paquier <michael(dot)paquier(at)gmail(dot)com> wrote:
>>
>> On Thu, Jun 25, 2015 at 12:57 PM, Fujii Masao wrote:
>> > On Thu, Jun 25, 2015 at 12:15 PM, Michael Paquier wrote:
>> >> and that's actually equivalent to that in
>> >> the grammar: 1(AAA,BBB,CCC).
>> >
>> > I don't think that they are the same. In the case of 1(AAA,BBB,CCC),
>> > while
>> > two servers AAA and BBB are running, the master server may return a
>> > success
>> > of the transaction to the client just after it receives the ACK from
>> > BBB.
>> > OTOH, in the case of AAA,BBB, that never happens. The master must wait
>> > for
>> > the ACK from AAA to arrive before completing the transaction. And then,
>> > if AAA goes down, BBB should become synchronous standby.
>>
>> Ah. Right. I missed your point, that's a bad day... We could have
>> multiple separators to define group types then:
>> - "()" where the order of acknowledgement does not matter
>> - "[]" where it does not.
>> You would find the old grammar with:
>> 1[AAA,BBB,CCC]
>
> Let's start with a complex, fully described use case then work out how to
> specify what we want.
>
> I'm nervous of "it would be good ifs" because we do a ton of work only to
> find a design flaw.
>

I'm not sure specific implementation yet, but I came up with solution
for this case.

For example,
- s_s_name = '1(a, b), c, d'
The priority of both 'a' and 'b' are 1, and 'c' is 2, 'd' is 3.
i.g, 'b' and 'c' are potential sync node, and the quorum commit is
enable only between 'a' and 'b'.

- s_s_name = 'a, 1(b,c), d'
priority of 'a' is 1, 'b' and 'c' are 2, 'd' is 3.
So the quorum commit with 'b' and 'c' will be enabled after 'a' down.

With this idea, I think that we could use conventional syntax as in the past.
Though?

Regards,

--
Sawada Masahiko