Re: Sync Rep: First Thoughts on Code

Greetings!

On Fri, Dec 5, 2008 at 6:59 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
>
> On Fri, 2008-12-05 at 16:00 +0900, Fujii Masao wrote:
>
>> On Fri, Dec 5, 2008 at 12:09 PM, Fujii Masao <masao.fujii@gmail.com> wrote:
>> >> I was expecting you to have walreceiver and startup share an end of WAL
>> >> address via shared memory, so that startup never tries to read past end.
>> >> That way we would be able to begin reading a WAL file *before* it was
>> >> filled. Waiting until a file fills means we still have to have
>> >> archive_timeout set to ensure we switch regularly.
>> >
>> > You mean that not pg_standby but startup process waits for the next
>> > WAL available? If so, I agree with you in the future. That is, I just think
>> > that this is next TODO because there are many problems which we
>> > should resolve carefully to achieve it. But, if it's essential for 8.4, I will
>> > tackle it. What is your opinion? I'd like to clear up the goal for 8.4.
>>
>> Umm.. on second thought, this feature (continuous recovery without
>> pg_standby) seems to be essential for 8.4. So, I will try it.
>
> Sounds good. Perhaps you can share what changed your mind in those 4
> hours...

Yeah, it's my imagination about the real situation after 8.4 release,
especially I considered about the future conjugal life of Synch Rep and
Hot Standby ;) Waiting to redo until the file fills might lead to marital
breakdown.

>
> Could we start with pictures and some descriptions first, so we know
> we're on the right track? I foresee no coding issues.
>
> My understanding is that we start with a normal log shipping
> architecture, then we switch into continuous recovery mode. So we do use
> pg_standby at beginning, but then it gets turned off.

Yes, I also understand so. Updated sequence pictures are on wiki
as per usual. Please see P3, 4.
http://wiki.postgresql.org/wiki/NTT%27s_Development_Projects#Detailed_Design

>
> Let's look at all of the corner cases also:
> * standby keeps pace with primary (desired state)
> * standby falls behind primary
> * standby restarts to change shmmem settings
> etc

Yes, I will examine such cases!

Regards,

-- 
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center