Re: retry shm attach for windows (WAS: Re: [HACKERS] OK, so culicidae is *still* broken) - Mailing list pgsql-hackers

From Tom Lane
Subject Re: retry shm attach for windows (WAS: Re: [HACKERS] OK, so culicidae is *still* broken)
Date
Msg-id 32199.1496670993@sss.pgh.pa.us
Whole thread Raw
In response to Re: retry shm attach for windows (WAS: Re: [HACKERS] OK, so culicidaeis *still* broken)  (Amit Kapila <amit.kapila16@gmail.com>)
Responses Re: retry shm attach for windows (WAS: Re: [HACKERS] OK, so culicidaeis *still* broken)
[HACKERS] Re: retry shm attach for windows (WAS: Re: OK, so culicidae is*still* broken)
List pgsql-hackers
Amit Kapila <amit.kapila16@gmail.com> writes:
> Sure.  I think it is slightly tricky because specs don't say clearly
> how ASLR can impact the behavior of any API and in my last attempt I
> could not reproduce the issue.

> I can try to do basic verification with the patch you have proposed,
> but I fear, to do the actual tests as suggested by you is difficult as
> it is not reproducible on my machine, but I can still try.

Yeah, being able to reproduce the problem reliably enough to say whether
it's fixed or not is definitely the sticking point here.  I have some
ideas about that:

1. Be sure to use Win32 not Win64 --- the odds of a failure in the larger
address space are so small you'd never prove anything.  (And of course
it has to be a version that has ASLR enabled.)

2. Revert 7f3e17b48 so that you have an ASLR-enabled build.

3. Crank shared_buffers to the maximum the machine will allow, reducing
the amount of free address space and improving the odds of a collision.

4. Spawn lots of sessions --- pgbench with -C option might be a useful
testing tool.

With luck, that will get failures often enough that you can be pretty
sure whether a patch improves the situation or not.
        regards, tom lane



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