From: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com> |
---|---|
To: | Amit Kapila <amit(dot)kapila(at)huawei(dot)com> |
Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: [PATCH] Patch to compute Max LSN of Data Pages |
Date: | 2012-11-14 16:48:51 |
Message-ID: | CAHGQGwFUM8cL9cwCGuwtLVoLvzsjq035mbTrGufwqjQBk_2GKQ@mail.gmail.com |
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Lists: | pgsql-hackers |
On Thu, Nov 15, 2012 at 12:55 AM, Amit Kapila <amit(dot)kapila(at)huawei(dot)com> wrote:
> Now user can use this utility to decide if new-standby has max LSN greater
> than max LSN of new-master he needs to use fullback-up on new-standby. Is my
> understanding right?
No. The maximum LSN of data pages in new-standby should be compared with
the last replayed LSN (IOW, the last valid LSN of previous timeline)
of new-master.
>>OTOH, there can be the case
>> where new master has already been ahead of the startpoint.
>
>
> But in this case, there is no need for this utility. Right?
No. The above comparison is required in this case.
>
>> > So now user may not be able to decide whether he needs to do
>> incremental or
>> > full backup from new master,
>> > is this the case you are trying to point?
>>
>> Sorry, I could not parse this comment. Could you elaborate your concern
>> again?
>
> I wanted to understand the usecase mentioned by you for this utility.
> As far as I can understand is that it will be used to decide that on
> new-standby (old-master) whether a full backup is needed from
> New-master(old-standby).
Yes.
> And that situation can occur when new-standby has startpoint LSN greater
> than new-master?
Whether the backup is required has nothing to do with the startpoint.
The backup is required when the data page in old-master precedes
the last applied LSN in old-standby (i.e., new-master) at the moment
of the failover. Without the backup, there is no way to revert the data
which is ahead of new-master.
Regards,
--
Fujii Masao
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