From: Roberto Garcia <roberto.garcia@cptec.inpe.br>
Cc: pgsql-admin@postgresql.org
Subject: Re: Major upgrade advice
Date: Fri, 20 Jun 2008 11:06:01 -0300
Message-ID: <485BB949.8040504@cptec.inpe.br> (raw)
In-Reply-To: <485B57D6.4040702@alreg.no>
References: <48594429.7040001@pinpointresearch.com>
<48595B63.4080000@cptec.inpe.br>
<!&!AAAAAAAAAAAYAAAAAAAAAN6d+lQFliBLjc3jO6z0BSQigQAAEAAAANXsptp1/mNJkA+ZsX3eKygBAAAAAA==@tcscs.com>
<485AABC9.3020807@cptec.inpe.br>
<485B57D6.4040702@alreg.no>
Curiosity is good, I also did some tests here, with yours and the syntax
suggested by "Achilleas Mantzios" and the results were:
1ST TEST
-----------------------------------------------------------------------------------------------------------------------------------------------------------------
The table has ~930000 rows, query returns ~33000 rows (results from one day)
Column is timestamp without time zone.
There is an index on timestamp_column
The result is the average of running 10 times each SELECT.
SELECT * FROM xxx WHERE (tscol) >= '2007-05-20 00:00:00' AND (tscol) <=
'2008-05-20 23:59:59';
--> .478" (3rd place)
SELECT * FROM xxx WHERE (tscol) BETWEEN '2007-05-20 00:00:00' AND
'2008-05-20 23:59:59';
--> .475" (1st place)
SELECT * FROM xxx WHERE (tscol) >= CAST('2007-05-20' as timestamp) AND
(tscol) < CAST('2008-05-21' as timestamp);
--> .483" (4th place)
SELECT * FROM xxx WHERE (tscol)::date = '2008-05-20'::date;
--> .476" (2nd place)
2ND TEST
-----------------------------------------------------------------------------------------------------------------------------------------------------------------
The table has ~930000 rows, query returns ~196000 rows (results from
five days)
SELECT * FROM xxx WHERE (tscol) >= '2007-05-20 00:00:00' AND (tscol) <=
'2008-05-25 23:59:59';
--> 2.477" (1st place)
SELECT * FROM xxx WHERE (tscol) BETWEEN '2007-05-20 00:00:00' AND
'2008-05-25 23:59:59';
--> 2.540" (4th place)
SELECT * FROM xxx WHERE (tscol) >= CAST('2007-05-20' as timestamp) AND
(tscol) < CAST('2008-05-26' as timestamp);
--> 2.512" (3dr place)
SELECT * FROM xxx WHERE (tscol)::date >= '2008-05-20'::date AND
(tscol)::date <= '2008-05-25'::date;
--> 2.482" (2nd place)
- The 4th SELECT was a surprise, how could it was so fast if it does not
use the index?
- Creating an additional index needs to be studied carefully because our
tables are huge and indexes are already consuming ~1/3 of the size of
tables.
Regards
Roberto Garcia
Jan-Ivar Mellingen wrote:
> I got curious and did a few tests on a 8.3.3 database on my laptop.
> The 3 different queries all worked, but one took twice as long.
>
> The table alarmlogg has ~930000 rows, query returns ~260000 rows.
> Column alarm_tid is timestamp with time zone.
> There is an index on alarm_tid.
>
> select * from alarmlogg where alarm_tid between '2007-05-20 00:00:00'
> and '2008-05-20 23:59:59';
> --> 152 seconds.
>
> select * from alarmlogg where (alarm_tid >= '2007-05-20 00:00:00') and
> (alarm_tid <= '2008-05-20 23:59:59');
> --> 151 seconds.
>
> SELECT * FROM alarmlogg WHERE alarm_tid >= CAST('2007-05-20' as
> timestamp) AND alarm_tid < CAST('2008-05-21' as timestamp);
> --> 301 seconds.
>
> I am using the syntax in the second example in my programs. It has
> worked since 8.0.
>
> Regards
> Jan-Ivar Mellingen
>
>
> Roberto Garcia skrev:
>> We changed it because 8.3 doesn't allow the operator LIKE on
>> timestamp columns. Your syntax works fine but we weren't used to use
>> as u do. There weren't any specific reason, only another way to do that.
>>
>> I think when we read that operator LIKE and timestamp values were
>> incompatible we assumed that timestamp values couldn't be compared to
>> any char value, opposed as your syntax is.
>>
>> We've tried to do "select * from X where <timestamp column> =
>> '2008-05-20 10:'", expecting that the result would be any minute from
>> 10 o'clock (10:15, 10:30, 10:45, etc) of the specific date, but this
>> syntax retrieves only 10:00 from that date.
>>
>> Tks for the new syntax.
>>
>> Regards
>> Roberto Garcia
>>
>> Gregory S. Youngblood wrote:
>>> That's a pretty substantial change. Why did you have to make this
>>> change?
>>> Was it causing syntax errors or to get better performance on those
>>> types of
>>> queries? Actually, now that I think about it, didn't:
>>> select * from X where <timestamp column> between '2008-05-20
>>> 00:00:00' and
>>> '2008-05-20 23:59:59' work? I could have sworn I have used that
>>> syntax in 8.2 without having to
>>> arbitrarily cast the arguments... now I'm going to have to go look. :)
>>>
>>> Yup, confirmed, 8.2.7 and no casting on the date arguments when I
>>> was using
>>> between.
>>>
>>> I'm just curious if there was a specific reason (i.e. better
>>> performance,
>>> better use of indexes, etc.) for your syntax.
>>>
>>> Thanks,
>>> Greg
>>>
>>> -----Original Message-----
>>> From: pgsql-admin-owner@postgresql.org
>>> [mailto:pgsql-admin-owner@postgresql.org] On Behalf Of Roberto Garcia
>>> Sent: Wednesday, June 18, 2008 12:01 PM
>>> Cc: pgsql-admin@postgresql.org
>>> Subject: Re: [ADMIN] Major upgrade advice
>>>
>>> Just to mention one issue we had here:
>>>
>>> In 8.1 we did this to retrieve all data from a specific date:
>>> SELECT * FROM xxx
>>> WHERE <timestamp_column> LIKE '2008-05-20%'
>>>
>>> In 8.3 we had to change to:
>>> SELECT * FROM xxx
>>> WHERE <timestamp_column> >= CAST('2008-05-20' as timestamp) AND
>>> <timestamp_column> < CAST('2008-05-21' as timestamp)
>>>
>>> Regards
>>> Roberto Garcia
>>>
>>>
>>>
>>
>>
>> Roberto Garcia
>> Banco de Dados, MSc
>> Fone: (12) 3186-8405
Roberto Garcia
Banco de Dados, MSc
Fone: (12) 3186-8405
--
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--
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Subject: Re: Major upgrade advice
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