Re: [BUG] pg_basebackup from disconnected standby fails

On Mon, Oct 24, 2016 at 1:39 PM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> On Mon, Oct 24, 2016 at 9:18 AM, Kyotaro HORIGUCHI
> <horiguchi.kyotaro@lab.ntt.co.jp> wrote:
>> Thank you for looking and retelling this.

+1.

>> At Fri, 21 Oct 2016 13:02:21 -0400, Robert Haas <robertmhaas@gmail.com> wrote in
<CA+TgmoaRdyfCqcg9x-E99XCxdC4LW0zygP5qLsPhFsb6BYDKow@mail.gmail.com>
>>> I can think of two solutions that would be "tighter":
>>>
>>> 1. When performing a restartpoint, update the minimum recovery point
>>> to just beyond the checkpoint record.  I think this can't hurt anyone
>>> who is actually restarting recovery on the same machine, because
>>> that's exactly the point where they are going to start recovery.  A
>>> minimum recovery point which precedes the point at which they will
>>> start recovery is no better than one which is equal to the point at
>>> which they will start recovery.
>>
>> This is a candidate that I thought of. But I avoided to change
>> the behavior of minRecoveryPoint that (seems to me that) it
>> describes only buffer state. So checkpoint with no update doesn't
>> advances minRecoveryPoint as my understanding.
>
> I think what you are saying is not completely right, because we do
> update minRecoveryPoint when we don't perform a new restart point.
> When we perform restart point, then it assumes that flushing the
> buffers will take care of updating minRecoveryPoint.

Yep, minRecoveryPoint still gets updated when the last checkpoint
record is the last restart point to avoid a hot standby to allow
read-only connections at a LSN-point earlier than the last shutdown.
Anyway, we can clearly reject 1. in the light of
https://www.postgresql.org/message-id/CAA4eK1KmjtsXqF0cav7Cs4d4vwv2H_pc8d8q1BUCqDzAF+7EzQ@mail.gmail.com
when playing with different stop locations at recovery.
-- 
Michael