On Wed, Nov 30, 2016 at 7:53 PM, Amit Kapila <amit.kapil...@gmail.com> wrote: > On Mon, Nov 21, 2016 at 11:08 AM, Michael Paquier > <michael.paqu...@gmail.com> wrote: >> On Tue, Nov 15, 2016 at 9:59 PM, Amit Kapila <amit.kapil...@gmail.com> wrote: >>> On Tue, Nov 15, 2016 at 9:27 AM, Kyotaro HORIGUCHI >>> <horiguchi.kyot...@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. >> > > That's okay, but I think you are using it to skip switch segment stuff > as well. Today, again going through patch, I noticed small anomaly > >> + * Switch segment only when WAL has done some progress since the > + * > last time a segment has switched because of a timeout. > >> + if (GetProgressRecPtr() > last_switch_lsn) > > Either the above comment is wrong or the code after it has a problem. > last_switch_lsn aka XLogCtl->lastSegSwitchLSN is updated not only for > a timeout but also when there is a lot of WAL activity which makes WAL > Write to cross a segment boundary.
Right, this should be reworded a bit better to mention both. Done as attached. -- Michael
hs-checkpoints-v19.patch
Description: invalid/octet-stream
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