On Fri, May 26, 2017 at 5:30 AM, Tsunakawa, Takayuki
<tsunakawa.ta...@jp.fujitsu.com> wrote:
> From: pgsql-hackers-ow...@postgresql.org
>> [mailto:pgsql-hackers-ow...@postgresql.org] On Behalf Of Amit Kapila
>> Yes, I also share this opinion, the shm attach failures are due to
>> randomization behavior, so sleep won't help much.  So, I will change the
>> patch to use 100 retries unless people have other opinions.
> Perhaps I'm misunderstanding, but I thought it is not known yet whether the 
> cause of the original problem is ASLR.  I remember someone referred to 
> anti-virus software and something else.

We are here purposefully trying to resolve the randomize shm
allocation behavior due to ASLR.  The original failure was on a linux
machine and is resolved.  We presumably sometimes get the failures [1]
due to this behavior.

>  I guessed that the reason Noah suggested 1 - 5 seconds of retry is based on 
> the expectation that the address space might be freed by the anti-virus 
> software.

Noah is also suggesting to have a retry count, read his mail above in
this thread and refer to his comment ("Thus, measuring time is
needless complexity; retry count is a suitable proxy.")

I think the real question here is, shall we backpatch this fix or we
want to do this just in Head or we want to consider it as a new
feature for PostgreSQL-11.  I think it should be fixed in Head and the
change seems harmless to me, so we should even backpatch it.

[1] - https://www.postgresql.org/message-id/14121.1485360296%40sss.pgh.pa.us

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

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