Re: Patch for fail-back without fresh backup

On Thu, Sep 19, 2013 at 7:32 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
> On Thu, Sep 19, 2013 at 7:07 PM, Sawada Masahiko <sawada(dot)mshk(at)gmail(dot)com> wrote:
>> On Thu, Sep 19, 2013 at 12:25 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>>> On Thu, Sep 19, 2013 at 11:48 AM, Sawada Masahiko <sawada(dot)mshk(at)gmail(dot)com> wrote:
>>>> I attached the patch which I have modified.
>>>
>>> Thanks for updating the patch!
>>>
>>> Here are the review comments:
>>>
>>
>> Thank you for reviewing!
>>
>>> I got the compiler warning:
>>>
>>> syncrep.c:112: warning: unused variable 'i'
>>>
>>> How does synchronous_transfer work with synchronous_commit?
>>
>> The currently patch synchronous_transfer doesn't work when
>> synchronous_commit is set 'off' or 'local'.
>> if user changes synchronous_commit value on transaction, checkpointer
>> process can't see it.
>> Due to that, even if synchronous_commit is changed to 'off' from 'on',
>> synchronous_transfer doesn't work.
>> I'm planning to modify the patch so that synchronous_transfer is not
>> affected by synchronous_commit.
>
> Hmm... when synchronous_transfer is set to data_flush,
> IMO the intuitive behaviors are
>
> (1) synchronous_commit = on
> A data flush should wait for the corresponding WAL to be
> flushed in the standby
>
> (2) synchronous_commit = remote_write
> A data flush should wait for the corresponding WAL to be
> written to OS in the standby.
>
> (3) synchronous_commit = local
> (4) synchronous_commit = off
> A data flush should wait for the corresponding WAL to be
> written locally in the master.
>

It is good idea.
So synchronous_commit value need to be visible from other process.
To share synchronous_commit with other process, I will try to put
synchronous_commit
value into shared buffer.
Is there already the guc parameter which is shared with other process?
I tried to find such parameter, but there was not it.

Regards,

-------
Sawada Masahiko