Message-ID: <45EED472.2070303@archonet.com>
Date: Wed, 07 Mar 2007 15:04:18 +0000
From: Richard Huxton <dev@archonet.com>
User-Agent: IceDove 1.5.0.9 (X11/20061220)
MIME-Version: 1.0
To: Zoolin Lin <zoolin3g@yahoo.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Any advantage to integer vs stored date w. timestamp
References: <20070307145040.25582.qmail@web63311.mail.re1.yahoo.com>
In-Reply-To: <20070307145040.25582.qmail@web63311.mail.re1.yahoo.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

Zoolin Lin wrote:
> thanks for your reply
> 
>> Primary table is all integers like:
>> 
>> date id | num1 | num2 | num3 | num4 | num5 | num6 | num7 | num 8 
>> -------------------------------------------------------------------------------------------------
>>  primary key is on date to num->6 columns
> 
>>> What types are num1->8?
> 
> They are all integer

Hmm - not sure if you'd get any better packing if you could make some
int2 and put them next to each other. Need to test.

>> date_id | date w timestamp ----------------------------------------
>> 1 | 2007-2-15 Midnight 2         | 2007-2-15 1 am 3         |
>> 2007-2-15 2 am  etc for 24 hours each day
> 
>>> If you only want things accurate to an hour, you could lost the
>>> join and just store it as an int: 2007021500, 2007021501 etc.
> 
> Hmm yeh I could, I think with the amount of data in the db though it
> behooves me to use one of the date types, even if via lookup table.

You can always create it as a custom ZLDate type. All it really needs to 
be is an int with a few casts.

> So I guess I'm just not sure if I'm really gaining anything by using
> an integer  date id column and doing a join on a date lookup table,
> vs just making it a date w. timestamp column and having duplicate
> dates in that column.
> 
> I would imagine internally that the date w. timestamp is stored as
> perhaps a time_t type  plus some timezone information. I don't know
> if it takes that much more space, or there's a significant
> performance penalty in using it

It's a double or int64 I believe, so allow 8 bytes instead of 4 for your 
int.

> 2,500 rows per hour, with duplicate date columns, seems like it could
> add up though.

Well, let's see 2500*24*365 = 21,900,000 * 4 bytes extra = 83MB 
additional storage over a year.	Not sure it's worth worrying about.

-- 
   Richard Huxton
   Archonet Ltd