RE: Is table with b-tree index is still a heap table?
- From: "Powell, Mark" <mark.powell2@xxxxxx>
- To: ORACLE-L <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 2 Apr 2014 19:56:39 +0000
Nik, I agree with Hemant in that normally you want your tables to be heap
tables. Most tables should have a PK constraint defined on them and there are
some advantages to the optimizer to having the PK constraint defined rather
than just having an index. In Oracle it is possible to support a PK constraint
using either unique or non-unique indexes. Unless you need to use deferred
constraints I would use unique indexes to support my PK constraints.
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Chitale, Hemant K
Sent: Wednesday, April 02, 2014 1:25 AM
To: Nik Tek
Cc: ORACLE-L
Subject: RE: Is table with b-tree index is still a heap table?
If a Primary Key isn't part of the design, I wouldn't "force-fit" one.
In most applications 90-99% of the tables would be heap tables. IOTs are the
rare exception.
Hemant K Chitale
From: Nik Tek [mailto:niktek2005@xxxxxxxxx]
Sent: Wednesday, April 02, 2014 12:35 PM
To: Chitale, Hemant K
Cc: ORACLE-L
Subject: Re: Is table with b-tree index is still a heap table?
Thank you Hemant!
Can you please elaborate a bit on 4).
Is it because d) doesn't provide any advantage?
Is there an alternative in fixing the schema, in the current schema almost 40%
of the tables are straight heap tables or heap+index.
Thank you
Nik
On Tue, Apr 1, 2014 at 8:21 PM, Chitale, Hemant K
<Hemant-K.Chitale@xxxxxx<mailto:Hemant-K.Chitale@xxxxxx>> wrote:
1) Yes, a) is a heap table I know that, but b) is a heap table?
Yes, b) is a Heap Table PLUS an Index - the Table and Index are separate
objects.
2) Is there any advantage of bumping up the C1 column to PK, like storage,
performance?
It depends. Does C1 not have a Unique Index definition yet ? You probably
need to cleanup duplicates first. There is no storage benefit with a PK. A
PK, in itself, doesn't offer a performance benefit if there's already an index.
A PK is more about "clean" data and proper design.
3) Is b) and c) are the same?
No. b) has a heap table and a separate index. c) is an IOT.
4) Say my application is already out in the customers site, changing the C1 to
PK would be tricky, instead can do solution d) ?
I wouldn't advise it.
Hemant K Chitale
From: oracle-l-bounce@xxxxxxxxxxxxx<mailto:oracle-l-bounce@xxxxxxxxxxxxx>
[mailto:oracle-l-bounce@xxxxxxxxxxxxx<mailto:oracle-l-bounce@xxxxxxxxxxxxx>] On
Behalf Of Nik Tek
Sent: Wednesday, April 02, 2014 7:21 AM
To: oracle-l@xxxxxxxxxxxxx<mailto:oracle-l@xxxxxxxxxxxxx>
Subject: Is table with b-tree index is still a heap table?
Hi,
I have question about oracle heap tables vs. tables with b-tree index vs. IOT
tables.
Say I have a table T1
a) CREATE TABLE T1 (C1 NUMBER NOT NULL, C2 VARCHAR2(100));
b) CREATE TABLE T1 (C1 NUMBER NOT NULL, C2 VARCHAR2(100));
CREATE INDEX IDX_T1_C1 ON T1(C1);
c) CREATE TABLE T1 (C1 NUMBER NOT NULL, C2 VARCHAR2(100),
CONSTRAINT PK_T1_C1 PRIMARY KEY (C1) ORGANIZATION INDEX);
d)
CREATE SEQUENCE T1_SEQ INCREMENT BY 1;
/
ALTER TABLE T1
ADD SURR_KEY INTEGER NOT NULL;
/
ALTER TABLE T1
ADD CONSTRAINT PK_T1_C1_SK PRIMARY KEY (C1,SURR_KEY);
/
CREATE OR REPLACE TRIGGER T1_TRIG
BEFORE INSERT ON T1
FOR EACH ROW
BEGIN
SELECT T1_SEQ.nextval INTO :NEW.SURR_KEY FROM dual;
END;
Questions:
1) Yes, a) is a heap table I know that, but b) is a heap table?
2) Is there any advantage of bumping up the C1 column to PK, like storage,
performance?
3) Is b) and c) are the same?
4) Say my application is already out in the customers site, changing the C1 to
PK would be tricky, instead can do solution d) ?
Thank you
Nik
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