Re: retry shm attach for windows (WAS: Re: [HACKERS] OK, soculicidae is *still* broken)

On Wed, May 24, 2017 at 09:29:11AM -0400, Michael Paquier wrote:
> On Tue, May 23, 2017 at 8:14 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> > So it seems both you and Tom are leaning towards some sort of retry
> > mechanism for shm reattach on Windows.  I also think that is a viable
> > option to negate the impact of ASLR.  Attached patch does that.  Note
> > that, as I have mentioned above I think we need to do it for shm
> > reserve operation as well.  I think we need to decide how many retries
> > are sufficient before bailing out.  As of now, I have used 10 to have
> > some similarity with PGSharedMemoryCreate(), but we can choose some
> > different count as well.  One might say that we can have "number of
> > retries" as a guc parameter, but I am not sure about it, so not used.
> 
> New GUCs can be backpatched if necessary, though this does not seem
> necessary. Who is going to set up that anyway if we have a limit high
> enough. 10 looks like a sufficient number to me.

Ten feels low to me.  The value should be be low enough so users don't give up
and assume a permanent hang, but there's little advantage to making it lower.
I'd set it such that we give up in 1-5s on a modern Windows machine, which I
expect implies a retry count of one hundred or more.