On Wed, May 25, 2016 at 12:11 AM, Amit Kapila <amit.kapil...@gmail.com> wrote:
> On Tue, May 17, 2016 at 2:31 AM, Michael Paquier <michael.paqu...@gmail.com>
> wrote:
>>
>> On Tue, May 17, 2016 at 4:16 AM, Amit Kapila <amit.kapil...@gmail.com>
>> wrote:
>> > On Mon, May 16, 2016 at 9:45 AM, Michael Paquier
>> > <michael.paqu...@gmail.com>
>> > wrote:
>> >>
>> >> On Sun, May 15, 2016 at 3:34 PM, Amit Kapila <amit.kapil...@gmail.com>
>> >> wrote:
>> >> > Sounds sensible, but if we want to that route, shall we have some
>> >> > mechanism
>> >> > such that if retrying it for 10 times (10 is somewhat arbitrary, but
>> >> > we
>> >> > retry 10 times in PGSharedMemoryCreate, so may be there is some
>> >> > consistency)
>> >> > doesn't give us unique name and we are getting EACCES error, then
>> >> > just
>> >> > throw
>> >> > the error instead of more retries.  This is to ensure that if the API
>> >> > is
>> >> > returning EACCES due to reason other than duplicate handle, then we
>> >> > won't
>> >> > retry indefinitely.
>> >>
>> >> The logic in win32_shmem.c relies on the fact that a segment will be
>> >> recycled, and the retry is here because it may take time at OS level.
>> >> On top of that it relies on the segment names being unique across
>> >> systems. So it seems to me that it is not worth the complication to
>> >> duplicate that logic in the dsm implementation.
>> >
>> > If we don't do retry for fixed number of times, then how will we handle
>> > the
>> > case if EACCES is due to the reason other than duplicate handle?
>>
>> EACCES is a bit too low-level... I had in mind to check GetLastError
>> with only ERROR_ACCESS_DENIED, and retry only in this case, which is
>> the case where one postmaster is trying to access the segment of
>> another.
>>
>
> Okay, attached patch just does that and I have verified that it allows to
> start multiple services in windows.  In off list discussion with Robert, he
> suggested not to complicate the patch by retrying for fixed number of times
> as there is no proof that ERROR_ACCESS_DENIED can occur due to any other
> reason in this code path.  This patch is based on Kyotaro san's patch posted
> upthread with just minor changes in comments and indentation.

Thanks for catching Robert and getting confirmation on the matter. In
the same line of thoughts, I think as well that it is definitely not
worth complicating the retry logic in dsm.c, but you knew that already
per last week's discussion.

Regarding the patch, this looks good to me.
-- 
Michael


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