Thread: [BUGS] BUG #14838: clock_timestamp() returns same values for each row

The following bug has been logged on the website:

Bug reference:      14838
Logged by:          zam zam
Email address:      zam6ak@gmail.com
PostgreSQL version: 10rc1
Operating system:   Windows 10
Description:

Hello

We use clock_timestamp() function in our code and I have noticed that in PG
10 RC1 it returns same values across rows...

Here is the output from 9.6 compare to 10rc1

select version();
-- "PostgreSQL 9.6.3, compiled by Visual C++ build 1800, 64-bit"

select clock_timestamp() from generate_series(1,10)
-- "clock_timestamp"
-- "2017-09-29 09:39:34.820954-04"
-- "2017-09-29 09:39:34.820977-04"
-- "2017-09-29 09:39:34.820979-04"
-- "2017-09-29 09:39:34.820981-04"
-- "2017-09-29 09:39:34.820982-04"
-- "2017-09-29 09:39:34.820983-04"
-- "2017-09-29 09:39:34.820984-04"
-- "2017-09-29 09:39:34.820986-04"
-- "2017-09-29 09:39:34.820987-04"
-- "2017-09-29 09:39:34.820988-04"



select version();
-- "PostgreSQL 10rc1 on x86_64-pc-mingw64, compiled by gcc.exe (Rev5, Built
by MSYS2 project) 4.9.2, 64-bit"

select clock_timestamp() from generate_series(1,10)
-- "clock_timestamp"
-- "2017-09-29 09:38:45.779869-04"
-- "2017-09-29 09:38:45.779869-04"
-- "2017-09-29 09:38:45.779869-04"
-- "2017-09-29 09:38:45.779869-04"
-- "2017-09-29 09:38:45.779869-04"
-- "2017-09-29 09:38:45.779869-04"
-- "2017-09-29 09:38:45.779869-04"
-- "2017-09-29 09:38:45.779869-04"
-- "2017-09-29 09:38:45.779869-04"
-- "2017-09-29 09:38:45.779869-04"






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Jeff Janes <jeff.janes@gmail.com> writes:
> On Fri, Sep 29, 2017 at 6:43 AM, <zam6ak@gmail.com> wrote:
>> We use clock_timestamp() function in our code and I have noticed that in PG
>> 10 RC1 it returns same values across rows...

> Probably not an issue of the different versions, but rather different
> compilers (or maybe different hardware?).

AFAICS, our code in this area (see src/port/gettimeofday.c) has not
changed since 9.5.  I'm suspicious of a platform change.

> I get the same behavior on these two versions:
> ...
> and that behavior is that the timestamp jumps 500 usec at a time, despite
> looking as if it might have usec granularity:

What gettimeofday.c does is to use GetSystemTimePreciseAsFileTime()
if it can get hold of that, otherwise fall back to
GetSystemTimeAsFileTime().  I don't see anything very specific in
Windows' documentation about the resolution to be expected from either
one, but I wonder if the OP's 9.6 installation is using the former
while for some reason his 10rc1 installation is using the latter.
        regards, tom lane


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