Re: Fix checkpoint skip logic on idle systems by tracking LSN progress

On Tue, Nov 15, 2016 at 9:59 PM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> On Tue, Nov 15, 2016 at 9:27 AM, Kyotaro HORIGUCHI
> <horiguchi.kyotaro@lab.ntt.co.jp> wrote:
>> The term "WAL activity' is used in the comment for
>> GetProgressRecPtr. Its meaning is not clear but not well
>> defined. Might need a bit detailed explanation about that or "WAL
>> activity tracking". What do you think about this?
>>
>
> I would have written it as below:
>
> GetProgressRecPtr -- Returns the WAL progress.  WAL progress is
> determined by scanning each WALinsertion lock by taking directly the
> light-weight lock associated to it.

Not sure if that's better.. What about something as fancy as that?
 /*
- * Get the time of the last xlog segment switch
+ * GetProgressRecPtr -- Returns the newest WAL progress position.  WAL
+ * progress is determined by scanning each WALinsertion lock by taking
+ * directly the light-weight lock associated to it.  The result of this
+ * routine can be compared with the last checkpoint LSN to check if
+ * a checkpoint can be skipped or not.
+ *
It may be worth mentioning that the result of this routine is
basically used for checkpoint skip logic.
--
Michael