Re: retry shm attach for windows (WAS: Re: OK, so culicidae 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(dot)kapila16(at)gmail(dot)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.