Re: Sync Rep: First Thoughts on Code

Hi, sorry for my consecutive posting.

On Fri, Dec 5, 2008 at 4:00 PM, Fujii Masao <masao.fujii@gmail.com> wrote:
> Hello,
>
> 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.
>
> Development plan:
> - Share the end of WAL address via shared memory <--- Done!
> - Change ReadRecord() to wait for the next WAL *record* available.
> - Change ReadRecord() to restore the WAL from archive by using
>  pg_standby before reaching the replication starting position, then
>  read the half-streaming WAL from pg_xlog.
> - Add new trigger for promoting the standby to the primary. As the
>  trigger, when fast shudown (SIGINT) is requested during recovery,
>  the standby would recover the WAL up to end and become the
>  primary.
>
> What system call does walreceiver have to call against the WAL
> before startup process reads it? Probably we need  to call write(2),
> and don't need fsync(2) in Linux. How about other platform?

I added the figures about the latest architecture into PDF file.
Please check P6, 7. Is this architecture close to your imege?
http://wiki.postgresql.org/wiki/NTT%27s_Development_Projects#Detailed_Design

Regards,

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