Re: [HACKERS] Date/time on glibc2 linux

> The following gave me wrong result:
> I am pretty sure date/time arithmetic on Postgres should be changed
> accordingly. Where can I start in postgres sources? Anyone to help?

I see the same symptom on my RH5.1 (glibc2) box here:

lockhart=> select datetime('today'::date);
datetime
----------------------------
Fri Dec 04 06:00:00 1998 MSK
(1 row)

Whereas my RH4.2 (libc5) box gets it right:

postgres=> select datetime('today'::date);
datetime
----------------------------
Fri Dec 04 00:00:00 1998 MSK
(1 row)

This isn't specific to your timezone; I see the same problem with
PST8PST. The routine actually getting invoked is date_datetime() in
backend/utils/adt/datetime.c. I would be reluctant to scatter
glibc2-specific bug-fix code throughout the date/time files (the issue
has come up before), but once we've identified the actual cause of the
problem we can consider a workaround.

To help look at the problem do a "make clean" in that directory, and
modify the Makefile to add to CFLAGS the argument "-DDATEDEBUG" which
will enable some print statements.

If it is a glibc2 bug then presumably someone will be applying a fix to
that fairly soon. If that is the case perhaps we can either
automatically test for the deficiency in configure or we can post the
fix as a patch rather than putting it into the main source tree.

btw, can you see a problem in the regression tests? I wonder if there
are other date/time routines which show problems. I don't usually run
Postgres regression tests on my RH5.1 box since that is at work...

- Tom

RH4.2 (libc-5.3.12):

postgres=> select datetime(current_date, '11:00');
datetime
----------------------------
Fri Dec 04 11:00:00 1998 MSK
(1 row)

postgres=> select 'now'::datetime;
?column?
----------------------------
Fri Dec 04 09:18:43 1998 MSK
(1 row)

RH5.1 (glibc-2.0.7):

lockhart=> select datetime(current_date, '11:00');
datetime
----------------------------
Fri Dec 04 17:00:00 1998 MSK
(1 row)

lockhart=> select 'now'::datetime;
?column?
----------------------------
Fri Dec 04 09:16:21 1998 MSK
(1 row)