Re: Time-Delayed Standbys

(2013/12/12 18:09), Simon Riggs wrote:
> On 9 December 2013 10:54, KONDO Mitsumasa <kondo(dot)mitsumasa(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>> (2013/12/09 19:35), Pavel Stehule wrote:
>>>
>>>
>>>
>>>
>>> 2013/12/9 KONDO Mitsumasa <kondo(dot)mitsumasa(at)lab(dot)ntt(dot)co(dot)jp
>>> <mailto:kondo(dot)mitsumasa(at)lab(dot)ntt(dot)co(dot)jp>>
>>>
>>>
>>> Hi Fabrízio,
>>>
>>> I test your v4 patch, and send your review comments.
>>>
>>> * Fix typo
>>> > 49 -# commited transactions from the master, specify a recovery
>>> time delay.
>>> > 49 +# committed transactions from the master, specify a recovery
>>> time delay.
>>>
>>> * Fix white space
>>> > 177 - if (secs <= 0 && microsecs <=0)
>>> > 177 + if (secs <= 0 && microsecs <=0 )
>>>
>>> * Add functionality (I propose)
>>> We can set negative number at min_standby_apply_delay. I think that
>>> this feature
>>> is for world wide replication situation. For example, master server is
>>> in
>>> Japan and slave server is in San Francisco. Japan time fowards than
>>> San
>>> Francisco time
>>> . And if we want to delay in this situation, it can need negative
>>> number in
>>> min_standby_apply_delay. So I propose that time delay conditional
>>> branch
>>> change under following.
>>> > - if (min_standby_apply_delay > 0)
>>> > + if (min_standby_apply_delay != 0)
>>> What do you think? It might also be working collectry.
>>>
>>>
>>> what using interval instead absolute time?
>>
>> This is because local time is recorded in XLOG. And it has big cost for
>> calculating global time.
>
> I agree with your request here, but I don't think negative values are
> the right way to implement that, at least it would not be very usable.
I think that my proposal is the easiest and simplist way to solve this problem.
And I believe that the man who cannot calculate the difference in time-zone
doesn't set replication cluster across continents.

> My suggestion would be to add the TZ to the checkpoint record. This
> way all users of WAL can see the TZ of the master and act accordingly.
> I'll do a separate patch for that.
It is something useful for also other situations. However, it might be
going to happen long and complicated discussions... I　think that our hope is to
commit this patch in this commit-fest or next final commit-fest.

Regards,
--
Mitsumasa KONDO
NTT Open Source Software Center