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

On Tue, Jun 6, 2017 at 10:14 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> I think the idea of retrying process creation (and I definitely agree
>> with Tom and Magnus that we have to retry process creation, not just
>> individual mappings) is a good place to start.  Now if we find that we
>> are having to retry frequently, then I think we might need to try
>> something along the lines of what Andres proposed and what nginx
>> apparently did.  However, any fixed address will be prone to
>> occasional failures (or maybe, on some systems, regular failures) if
>> that particular address happens to get claimed by something.  I don't
>> think we can say that there is any address where that definitely won't
>> happen.  So I would say let's do this retry thing first, and then if
>> that proves inadequate, we can also try moving the mappings to a range
>> where conflicts are less likely.
>
> By definition, the address range we're trying to reuse worked successfully
> in the postmaster process.  I don't see how forcing a specific address
> could do anything but create an additional risk of postmaster startup
> failure.
>

I think it won't create an additional risk, because the idea is that
if we fail to map the shm segment at a predefined address, then we
will allow the system to choose the initial address as we are doing
now.  So, it can reduce chances of doing retries.

-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com