Thread
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Re: 'epoch'::timestamp and Daylight Savings
Hosen, John <john.hosen@capita.co.uk> — 2002-10-23T15:58:40Z
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. 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Re: 'epoch'::timestamp and Daylight Savings
lockhart@fourpalms.org — 2002-10-23T18:06:39Z
> 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 -
Re: 'epoch'::timestamp and Daylight Savings
Tom Lane <tgl@sss.pgh.pa.us> — 2002-10-23T18:46:33Z
"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