Oracle FAQ | Your Portal to the Oracle Knowledge Grid |
![]() |
![]() |
Home -> Community -> Mailing Lists -> Oracle-L -> Re: PK field - number of char
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
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
![]() |
![]() |