Re: [HACKERS] Re: [HACKERS] Re: [HACKERS] Windows service is not starting so there’s message in log: FATAL: "could not create shared memory segment “Global/PostgreSQL.851401618”: Permission denied”

On Thu, Mar 10, 2016 at 5:30 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Wed, Mar 9, 2016 at 7:16 AM, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com> wrote:
>> On Wed, Mar 9, 2016 at 10:06 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>>> On Wed, Mar 9, 2016 at 11:46 AM, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>
>>> wrote:
>>>>
>>>>
>>>> I tried replacing the random() with PostmaterRandom() for a test and it
>>>> worked.
>>>> This is generating different random values, so the issue is not occurring.
>>>>
>>>> "Global/PostgreSQL.2115609797"
>>>>
>>>> I feel, we should add the the data directory path + the random number to
>>>> generate the name for dynamic shared memory, this can fix problem.
>>>>
>>>
>>> As mentioned above, I think if we can investigate why this error is
>>> generated, that will be helpful. Currently the code ensures that if the
>>> segment already exists, it should retry to create a segment with other name
>>> (refer dsm_impl_windows()), so the point of investigation is, why it is not
>>> going via that path? I am guessing due to some reason CreateFileMapping()
>>> is returning NULL in this case whereas ideally it should return the existing
>>> handle with an error ERROR_ALREADY_EXISTS.
>>
>> DEBUG: mapped win32 error code 5 to 13
>>
>> Yes, the CreateFileMapping() is returning NULL with an error of
>> ERROR_ACCESS_DENIED.
>> I am not able to find the reason for this error. This error is occurring only
>> when the PostgreSQL is started as a service only.
>
> Another question is: why are both postmasters returning the same
> random number? That's not very, uh, random.

The random number is generated from our own implementation of
random function. The random function internally calls the pg_lrand48
function to get the random value. This function generates the random
number based on specified random seed and pre-defined calculations.
Because of this reason, the same random number is getting generated
every time.

In LInux, the random function is used from the glibc, there also it is
generating the same random number as the first number, but if the
number is used by some process then it is generating a different random
number for the next PostgreSQL process.

Regards,
Hari Babu
Fujitsu Australia