Re: New trigger option of pg_standby

Hi Simon,

Thanks for the comments!

On Thu, Apr 16, 2009 at 2:56 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
>
> On Wed, 2009-04-15 at 17:02 +0900, Fujii Masao wrote:
>
>> On Tue, Apr 14, 2009 at 2:41 PM, Fujii Masao <masao.fujii@gmail.com> wrote:
>> > I'd like to propose another simple idea; pg_standby deletes the
>> > trigger file *whenever* the nextWALfile is a timeline history file.
>> > A timeline history file is restored at the end of recovery, so it's
>> > guaranteed that the trigger file is deleted whether nextWALfile
>> > exists or not.
>> >
>> > A timeline history file is restored also at the beginning of
>> > recovery, so the accidentally remaining trigger file is deleted
>> > in early warm-standby as a side-effect of this idea.
>>
>> Here is the revised patch as above.
>>
>> If you notice something, please feel free to comment.
>
> Deleting the trigger file when we request a history file works in most
> cases, but not in all. We also request a history file when we switch
> timelines, so code comments need slight modification.
>
> If take a base backup, switchover and then try to regen the primary from
> the base backup we would need to switch timelines, which could be
> problematic. That is unlikely, so we should at least very clearly
> document the actual behaviour, as we do in the code comments.

"switch timelines" means that a new timeline ID is assigned at
the end of archive recovery? If so, even in this case, there is
no problem with deleting the trigger file, I think.
Or, am I misunderstanding?

> I think your wording that smart mode guarantees no data will be lost is
> a little strong. I'd say "on successful completion all WAL records will
> be replayed resulting in zero data loss".

Sounds good. I'll change the wording.

Regards,

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