Thomas,

Thanks for replying so quickly.

Upon some further investigation, the conversion of the time to BST is OK on
data inserted before the upgrade (the display was just a red herring), the
problem is just on new data inserted into the table with a default value for
the timestamp fields.

The output from \d on the table is below:

capitaras_live=# \d e_application
                                               Table "e_application"
      Column       |           Type           |
Modifiers                              
-------------------+--------------------------+-----------------------------
---------------------------------------
 e_app_id_num      | integer                  | not null default
nextval('"e_application_e_app_id_num_seq"'::text)
 e_app_cand_id_num | integer                  | 
 e_app_job_id      | character varying(30)    | not null
 e_app_cid_num     | bigint                   | 
 e_app_cts         | character varying(30)    | 
 e_app_mts         | character varying(30)    | 
 e_app_print_date  | timestamp with time zone | default
"timestamp"('epoch'::text)
 e_app_xfer_date   | timestamp with time zone | default
"timestamp"('epoch'::text)
 e_app_completed   | character varying(6)     | 
 e_app_xml         | text                     | 
 e_app_modified    | timestamp with time zone | 
 e_app_created     | timestamp with time zone | 
 e_app_wd_feedback | text                     | 
 e_app_submitted   | timestamp with time zone | 
Indexes: e_app_completed_idx,
         e_app_job_id_and_completed_idx
Primary key: e_application_pkey
Triggers: RI_ConstraintTrigger_27961

With a bit more playing, it definitely looks like something wrong with the
way the default value has been set follwing the export & import for the
upgrade:-

Create table arnold (
	a	int8,
	b	timestamp default 'epoch'::timestamp,
	c	timestamp default "timestamp"('epoch'::text)
);

capitaras_test=# \d arnold
                                  Table "arnold"
 Column |           Type           |                   Modifiers

--------+--------------------------+----------------------------------------
-------
 a      | bigint                   | 
 b      | timestamp with time zone | default '1970-01-01
01:00:00+01'::timestamptz
 c      | timestamp with time zone | default "timestamp"('epoch'::text) 

capitaras_test=# insert into arnold (a) values (1);
INSERT 182907 1
capitaras_test=# insert into arnold (a) values (2);
INSERT 182907 1

capitaras_test=# set timezone to 'Europe/London';
SET VARIABLE
capitaras_test=# select * from arnold;
 a |           b            |           c            
---+------------------------+------------------------
 1 | 1970-01-01 01:00:00+01 | 1970-01-01 00:00:00+01
 2 | 1970-01-01 01:00:00+01 | 1970-01-01 00:00:00+01
(2 rows)

capitaras_test=# set timezone to 'GMT';
SET VARIABLE
capitaras_test=# select * from arnold
capitaras_test-# ;
 a |           b            |           c            
---+------------------------+------------------------
 1 | 1970-01-01 00:00:00+00 | 1969-12-31 23:00:00+00
 2 | 1970-01-01 00:00:00+00 | 1969-12-31 23:00:00+00
(2 rows)


I think that the best way forward for us (short of re-writing the backend to
use NULL) will be to just alter the default value to the one in column b in
the test table above.

With regards the disclaimer, don't you just love lawyers ;-)

Once again, thanks for replying so quickly.

Regards

John.



-----Original Message-----
From: Thomas Lockhart [mailto:lockhart@fourpalms.org] 
Sent: 23 October 2002 16:06
To: Hosen, John
Cc: 'pgsql-hackers@postgresql.org'
Subject: Re: 'epoch'::timestamp and Daylight Savings


> We have just upgraded from 7.1.3 to 7.2.3 over the weekend, and have 
> just noticed something weird with regards 'epoch'::timestamp. In 
> 7.1.3, 'epoch'::timestamp always returned the value 1970-01-01 
> 00:00:00+00,...

I would expect 'epoch'::timestamp to always act as though the value were 
the same as Unix time zero. But it did not explicitly return that value:

lockhart=# select version();
-------------------------------------------------------------
  PostgreSQL 7.1.2 on i686-pc-linux-gnu, compiled by GCC 2.96

lockhart=# select 'epoch'::timestamp;
----------
  epoch

lockhart=# select 'epoch'::timestamp + '0 sec'::interval;
------------------------
  1969-12-31 16:00:00-08


> following the upgrade we now get:-
>       timestamptz       
> ------------------------
>  1970-01-01 01:00:00+01

Which is consistant with the previous result in absolute time.

You will find that the most recent versions of PostgreSQL convert 
'epoch' on input, and that with- and without time zone data types are 
available:

lockhart=# select cast('epoch' as timestamp with time zone);
       timestamptz
------------------------
  1969-12-31 16:00:00-08

lockhart=# select cast('epoch' as timestamp without time zone);
       timestamp
---------------------
  1970-01-01 00:00:00


> Also, any fields set to 'epoch'::timestamp before the upgrade now return:-
>     e_app_xfer_date     
> ------------------------
>  1970-01-01 00:00:00+01
> If we issue a SET TIMEZONE TO 'GMT' the results are the same as for 
> the previous release.

Not sure about this one. What is the schema? Can you give an example 
where the time gets shifted by an hour?

> This is causing us a problem as we use epoch to indicate whether the 
> data has been processed, and to log the date and time of processing.

Using "special values" to indicate status can be troublesome, as you are 
finding. I'd suggest using NULL to indicate that a field is not known or 
not yet set.

> This email and any files attached to it are confidential and intended
> solely for the use of the individual or entity to whom they are
> addressed. If you have received this email in error please notify 
> the system manager.

Oops. Can you please confirm that we were the intended recipients? ;)

hth

                     - Thomas


This email has been scanned for all viruses by the MessageLabs SkyScan
service.


***********************************************************************

This email and any files attached to it are confidential and intended 
solely for the use of the individual or entity to whom they are
addressed. If you have received this email in error please notify 
the system manager.

The message and any files attached to it have been scanned by 
MIMEsweeper with Sophos Sweep and found to be free from all known
viruses.

Information on MIMEsweeper can be found at http://www.mimesweeper.com/

***********************************************************************


Wed, 23 Oct 2002 16:58:40 +0100
"Hosen, John" <John.Hosen@capita.co.uk>
Re: 'epoch'::timestamp and Daylight Savings
> Create table arnold (
> 	a	int8,
> 	b	timestamp default 'epoch'::timestamp,
> 	c	timestamp default "timestamp"('epoch'::text)
> );
> I think that the best way forward for us (short of re-writing the backend to
> use NULL) will be to just alter the default value to the one in column b in
> the test table above.

Hmm. The "timestamp"() call is forcing TIMESTAMP WITHOUT TIME ZONE, 
which then gets converted to TIMESTAMP WITH TIME ZONE (adding in your 
one hour offset), which is the default for the unadorned, unquoted 
'timestamp' type.

You can use something like

   cast('epoch'::text as timestamp with time zone)

to get what you want, and can use "timestamptz"() if you insist. But 
that is not recommended for direct use in schema definitions, even if 
pgsql chooses to use it for dump/reloads at the moment.

                - Thomas


Wed, 23 Oct 2002 18:06:39 +0000
Thomas Lockhart <lockhart@fourpalms.org>
Re: 'epoch'::timestamp and Daylight Savings
"Hosen, John" <John.Hosen@capita.co.uk> writes:

>  e_app_print_date  | timestamp with time zone | default
> "timestamp"('epoch'::text)

Yeah, there's your problem.  You are casting 'epoch' to type timestamp
without time zone, and thence to timestamp with time zone.  The first
step gives "midnight" and the second assumes that that means "midnight
local time".

For example, in US EST zone I get:

regression=# select "timestamp"('epoch'::text);
      timestamp
---------------------
 1970-01-01 00:00:00
(1 row)

regression=# select ("timestamp"('epoch'::text))::timestamptz;
       timestamp
------------------------
 1970-01-01 00:00:00-05
(1 row)

whereas what is wanted is

regression=# select "timestamptz"('epoch'::text);
      timestamptz
------------------------
 1969-12-31 19:00:00-05
(1 row)

So you can fix the problem just by setting the default to be
'epoch'::timestamptz.

The problem is probably related to the renaming we've been carrying out
to get closer to the SQL spec: "timestamp" now means timestamp without
time zone, which is not what it meant in older Postgres releases.

			regards, tom lane

Wed, 23 Oct 2002 14:46:33 -0400
Tom Lane <tgl@sss.pgh.pa.us>
Re: 'epoch'::timestamp and Daylight Savings 