Oracle-L: Re: PK field - number of char

From: Brian Haas <bhaas_at_musiciansfriend.com>
Date: Wed, 17 Apr 2002 14:53:21 -0800
Message-ID: <F001.00447508.20020417145321@fatcity.com>

Tom,

Well you got me sort of. I ran a few quick tests on a table with 500K rows. The return times were almost always identical. The main difference between a Pk with a number and a char/varchar is storage. a 40 digit number takes 4bytes of space. A 40 character string takes 10 bytes.

This translated into the character datatype moving 30 more bytes per query over sql*net than the number datatype. On a heavily used application hitting a backend Oracle DB via sql*net, those extra bytes could make a difference in response time. but I guess that is more of a network bottleneck than a database one. here are my results:
char(40) Pk:
Elapsed: 00:00:00.52
Execution Plan

0 SELECT STATEMENT Optimizer=CHOOSE (Cost=2 Card=1 Bytes=10) 1 0 INDEX (UNIQUE SCAN) OF 'PKTEST_CHAR_PK' (UNIQUE) (Cost=2 C

ard=1 Bytes=10)
Statistics

          0  recursive calls
          0  db block gets
          3  consistent gets
          0  physical reads
          0  redo size
        239  bytes sent via SQL*Net to client
        253  bytes received via SQL*Net from client
          3  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

number datatype:
Elapsed: 00:00:00.51
Execution Plan

0 SELECT STATEMENT Optimizer=CHOOSE (Cost=2 Card=1 Bytes=4) 1 0 INDEX (UNIQUE SCAN) OF 'PKTEST_PK' (UNIQUE) (Cost=2 Card=1

Bytes=4)
Statistics

          0  recursive calls
          0  db block gets
          3  consistent gets
          0  physical reads
          0  redo size
        218  bytes sent via SQL*Net to client
        246  bytes received via SQL*Net from client
          3  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

-Brian

On Wed, 2002-04-17 at 11:52, Mercadante, Thomas F wrote:
> All,
>
> Does anyone have any specific metrics demonstrating that a PK that is based
> on a number field is faster than a PK based on a character field?
>
> I've seen it mentioned a couple of times today under the "Design Question"
> topic.
>
> It doesn't make any sense to me that one or the other would be faster.
> After all, we are talking about comparison searches within the B-Tree index
> structure. Why searching down the tree for a number is any faster than a
> char is lost on me.
>

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Brian Haas
  INET: bhaas_at_musiciansfriend.com

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).

Received on Wed Apr 17 2002 - 17:53:21 CDT