Re: Support for N synchronous standby servers - take 2

Hello,

At Wed, 10 Feb 2016 11:25:49 +0900, Masahiko Sawada <sawada.mshk@gmail.com> wrote in
<CAD21AoCHytB88ZdC0899J7PLNTKWTg0gczC2M7dqLmK71vdY0w@mail.gmail.com>
> On Wed, Feb 10, 2016 at 9:18 AM, Michael Paquier
> <michael.paquier@gmail.com> wrote:
> > On Wed, Feb 10, 2016 at 2:57 AM, Fujii Masao <masao.fujii@gmail.com> wrote:
> >> On Wed, Feb 10, 2016 at 1:36 AM, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >>> Attached first version dedicated language patch (document patch is not yet.)
> >>
> >> Thanks for the patch! Will review it.
> >>
> >> I think that it's time to write the documentation patch.
> >>
> >> Though I've not read the patch yet, I found that your patch
> >> changed s_s_names so that it rejects non-alphabet character
> >> like *, according to my simple test. It should accept any
> >> application_name which we can use.
> >
> > Cool. Planning to look at it as well. Could you as well submit a
> > regression test based on the recovery infrastructure and submit it as
> > a separate patch? There is a version upthread of such a test but it
> > would be good to extract it properly.
> 
> Yes, I will implement regression test patch and documentation patch as well.
> 
> Attached latest version patch supporting s_s_names = '*'.
> Unlike currently behaviour a bit, s_s_names can have only one '*' character.
> e.g, The following setting will get syntax error.
> 
> s_s_names = '*, node1,node2'
> s_s_names = `2[node1, *, node2]`

We could use the setting s_s_names = 'node1, node2, *' as a
extended representation of old s_s_names. It tests node1, node2
as first and try any name if they failed. Similary, '2[node1,
node2, *]' is also meaningful.

> when we use '*' character as s_s_names element, we must set s_s_names
> like follows.
> 
> s_s_names = '*'
> s_s_names = '2[*]'
> 
> BTW, we've discussed about mini language syntax.
> IIRC, the syntax uses [] and () like,
> 'N[node1, node2, ...]', to define priority standbys.
> 'N(node1, node2, ...)', to define quorum standbys.
> And current patch behaves so.
> 
> Which type of parentheses should be used for this syntax to be more clarity?
> Or other character should be used such as <>, // ?

I believed that [] and {} are used respectively for no distinct
reason. I think symmetrical pair of characters is preferable for
readability. Candidate pairs in ascii characters are.

(), {}, [] <> 

{} might be a bit difficult to distinguish from [] on unclear
consoles :p

regards,

-- 
Kyotaro Horiguchi
NTT Open Source Software Center