1 IOT Internals Julian Dyke Independent Consultant Web Version juliandyke.com © 2005 Julian Dyke.

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IOTInternals

Julian Dyke

Independent Consultant

Web Version

juliandyke.com

© 2005 Julian Dyke

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© 2005 Julian Dyke

Agenda

Heap Organized Tables Index Organized Tables IOT Overflow IOT Secondary Indexes IOT Mapping Tables

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Heap Organized TablesIntroduction Tables can be

ORGANIZATION HEAP (default) ORGANIZATION INDEX (8.0 and above) ORGANIZATION EXTERNAL (9.0 and above)

By default all tables are heap organized

Heap organized tables are not sorted on any column

Rows can be located using a physical ROWID which comprises Relative tablespace number Block number Slot number

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Heap Organized TablesIndexes Indexes on heap organized tables can be

B*Tree indexes Bitmap indexes

B*Tree indexes contain Key (one or more table columns) Physical ROWID

Bitmap indexes contain Key (one or more table columns) Start ROWID End ROWID Bitmap

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Heap Organized TablesExecution Plans

CREATE TABLE team(

team_key VARCHAR2(3),team_name VARCHAR2(50),country_key VARCHAR2(3),CONSTRAINT team_pk PRIMARY KEY (team_key)

)ORGANIZATION HEAP;

INSERT INTO team VALUES (‘FER’, ’Ferrari’, ’ITA’);

SELECT team_name FROM teamWHERE team_key = ‘FER’;

SELECT STATEMENT TABLE ACCESS (BY INDEX ROWID) OF ‘TEAM’

INDEX (UNIQUE SCAN) OF ‘TEAM_PK’

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Heap Organized TablesExample Index Block

00 02 01 00 00 72 00 00 03 46 45 52

INSERT INTO team VALUES (‘FER’,’Ferrari’,’ITA’);

Row#0[8024] flag: -----, lock: 2, data 01 00 00 72 00 00col 0; len 3; (3): 46 45 52

Flag Lock Length Length

F E R

Index Row Header

Index Col 0

Table ROWID

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Heap Organized TablesExample Table Block

2C 01 03 03 46 45 52 07 46 65 72 72 61 72 69 03 49 54 41


Tab 0, row 0,@0x1f8dtl: 19 fb: --H-FL– lb: 0x1 cc: 3col 0: [ 3] 46 45 52 -- FERcol 1: [ 7] 46 65 72 72 61 72 69 -- Ferraricol 2: [ 3] 49 54 41 -- ITA

Table Row Header

Table Col 0

Table Col 0

Table Col 2

I T AF e r r a r iF E R

Flag Lock LengthLength Length#Cols

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Heap Organized TablesSummary Tables include

Three byte row header Table columns (including key columns)

Indexes include Two byte row header Redundant key columns Six byte ROWID

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Index Organised TablesIntroduction Introduced in Oracle 8.0

Must be declared as ORGANIZATION INDEX

Must have primary key constraint held in index row

Can contain non-key columns held in table row may be stored in overflow segment

Do not have table segment Do not store physical ROWIDs

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Index Organised TablesIntroduction Can be compressed Can be range or hash partitioned (8.1.5 and above) Can have secondary B*tree indexes (8.1.5 and above) Can have secondary bitmap indexes (9.2 and above) Can include LOBs in non-key columns Can include ADTs in non-key columns Can include ROWID columns

Cannot be reversed Cannot be list or composite partitioned Cannot contain LONG columns

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Index Organised TablesRestrictions Maximum number of primary key columns is 33 Maximum number of columns is 1000 Maximum primary key lengths in Oracle 9.2

Block Size Maximum Key Length

2048 755

4096 1575

8192 3215

16384 3800

Non-key column lengths are not restricted

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Index Organized TablesInline versus Out-of-Line Constraints Primary key constraint can be inline or out-of-line

CREATE TABLE team(

team_key VARCHAR2(3) PRIMARY KEY,team_name VARCHAR2(50),country_key VARCHAR2(3)

)ORGANIZATION INDEX;

CREATE TABLE team(



Out-of-line

Inline

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Index Organized TablesImplementation The statement

CREATE TABLE team(



CREATE UNIQUE INDEX “TEAM_PK” ON “TEAM” (“TEAM_KEY”)INDEX ONLY TOPLEVELTABLESPACE “TS01”NOPARALLEL;

generates the following recursive statement (10046)

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Index Organised TablesHeap tables versus IOTs

CREATE TABLE team(

team_key VARCHAR2(3),team_name VARCHAR2(50),country_key VARCHAR2(3)CONSTRAINT team_pkPRIMARY KEY (team_key);

)ORGANIZATION HEAP;

CREATE TABLE team(



Heap-organised table Index-organised table



SELECT STATEMENT INDEX (UNIQUE SCAN) OF ‘TEAM_PK’

SELECT STATEMENT TABLE ACCESS (BY INDEX ROWID) OF ‘TEAM’

INDEX (UNIQUE SCAN) OF ‘TEAM_PK’

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Index Organised TablesHeap tables versus IOTs

Root

Branch

Leaf

Table

CREATE TABLE team(


)ORGANIZATION HEAP;

CREATE TABLE team(




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Index Organized TablesSegments IOTs do not have table segments

Index segment name depends on primary key constraint

Out-of-line constraints Index segment name same as constraint name

Inline constraints Index segment name is

SYS_IOT_TOP_<objectid>

where objectid is object ID of IOT / IOT partition

e.g.

SYS_IOT_TOP_6650

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Index Organized TablesExample Index Block

04 02 03 46 45 52 2C 00 02 07 46 65 72 72 61 72 69 03 49 54 41


Row#0[8015] flag: K----, lock: 2col 0; len 3; (3): 46 45 52tl: 15 fb: --H-FL– lb: 0x0 cc: 2col 0: [ 7]Dump of memory from 0x05C92FB5 to 0x05C92FBC5C92FB0 72654607 69726172 [.Ferrari]col 1: [ 3]Dump of memory from 0x05C92FBD to 0x05C92FC05C92FB0 41544903 [.ITA]

Index Row Header

Index Col 0

Table Row Header

Table Col 0

Table Col 1

Flag Lock Length Flag Lock #Cols LengthLength


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Index Organized TablesHeap organised tables versus IOTs

04 02 03 46 45 52 2C 00 02 07 46 65 72 72 61 72 69 03 49 54 41

Index Row Header

Index Col 0

Table Row Header

Table Col 0

Table Col 1

00 02 01 00 01 E2 00 00 03 46 45 52

2C 01 03 03 46 45 52 07 46 65 72 72 61 72 69 03 49 54 41

Table Row Header

Table Col 0

Table Col 1

Table Col 2

Index Row Header

Index Col 0

TableROWID

Heap-organised table

Index-organised table

Index Row

Index Row

TableRow F E R

F E RF E R

F E R

I T AF e r r a r i

F e r r a r i I T A

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Index Organized TablesPhysical ROWIDs

CREATE TABLE team(



CREATE TABLE team(


)ORGANIZATION HEAP;

SELECT ROWID FROM team; SELECT ROWID FROM team;

ROWID

AAABvFAAEAAAADgAAAAAABvFAAEAAAADgAABAAABvFAAEAAAADgAACAAABvFAAEAAAADgAAD

ROWID

*BAEAAOoDQUdT/g*BAEAAOoDQUxG/g*BAEAAOoDQU1P/g*BAEAAOoDQU5E/g


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Index Organized TablesColumn Ordering If primary key columns are not first in table declaration, Oracle

will reorder columns within the segment

CREATE TABLE team(

team_name VARCHAR2(50),country_key VARCHAR2(3),team_key VARCHAR2(3) PRIMARY KEY

)ORGANIZATION INDEX

Column Name Column Type

team_name VARCHAR2(50)

country_key VARCHAR2(3)

team_key VARCHAR2(3)

DESCRIBE team

NAME COL# INTCOL# SEGCOL#

team_name 1 1 2

country_key 2 2 3

team_key 3 3 1

SYS.COL$

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Index Organized TablesColumn Ordering

04 02 03 46 45 52 2C 00 02 07 46 65 72 72 61 72 69 03 49 54 41

INSERT INTO team VALUES (’Ferrari’ ,’ITA’, ’FER’);

Row#0[8015] flag: K----, lock: 2col 0; len 3; (3): 46 45 52tl: 15 fb: --H-FL– lb: 0x0 cc: 2col 0: [ 7]Dump of memory from 0x05C92FB5 to 0x05C92FBC5C92FB0 72654607 69726172 [.Ferrari]col 1: [ 3]Dump of memory from 0x05C92FBD to 0x05C92FC05C92FB0 41544903 [.ITA]

Index Row Header

Index Col 0

Table Row Header

Table Col 0

Table Col 1



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Index Organised TablesSummary For SELECT statements

useful for lookup tables avoid additional logical I/O for non-key data reduce latching

Do not store physical ROWID Six bytes less storage required

Optionally can store non-key data Requires three byte table row header

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IOT OverflowIntroduction Introduced in Oracle 8.0

Inefficient to store long rows in index segment Store rarely accessed columns in overflow segment

Primary key rows always stored in index segment Non-key rows can stored in index segment or overflow Overflow segment is additional table segment Index row includes six byte ROWID for overflow row

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IOT OverflowPCTTHRESHOLD Clause Specifies percentage of space reserved in index block for IOT

row Must be large enough to hold primary key All columns causing threshold to be exceeded are stored in

overflow segment Syntax is

PCTTHRESHOLD threshold

where threshold is integer in the range 1..50 Default value is 50

CREATE TABLE team(

team_key VARCHAR2(3) PRIMARY KEY,team_name VARCHAR2(50),history VARCHAR2(4000)

)ORGANIZATION INDEXOVERFLOWPCTTHRESHOLD 5;

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IOT OverflowINCLUDING Clause Can be used to specify which columns are held on index

block Syntax is

INCLUDING column_name

where column_name can be last column of primary key any non-key column

CREATE TABLE team(

team_key VARCHAR2(3) PRIMARY KEY,team_name VARCHAR2(50),history VARCHAR2(4000)

)ORGANIZATION INDEXOVERFLOWINCLUDING team_name;

Column Name Column Type Block Type

team_key Primary Key Index Block

team_name Non-Key Index Block

history Non-Key Overflow Block

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IOT Overflow TablesSegments IOT Overflow Table segments are created automatically when

OVERFLOW clause is used

Overflow segment name is

where object_id is the object id of the IOT / IOT partition

Overflow segment cannot be directly accessed by SELECT, INSERT, UPDATE or DELETE operations

For partitioned IOTs, overflow segment is locally partitioned

SYS_IOT_OVER_<object_id>

SYS_IOT_OVER_6650

e.g.

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IOT OverflowExecution Plans

CREATE TABLE team(

team_key VARCHAR2(3),team_name VARCHAR2(50),history VARCHAR2(4000),CONSTRAINT team_pkPRIMARY KEY (team_key)

)ORGANIZATION INDEXOVERFLOWINCLUDING team_name;

SELECT team_name, historyFROM teamWHERE team_key = ‘FER’;

0 SELECT STATEMENT1 0 INDEX (UNIQUE SCAN) OF ‘TEAM_PK’

INSERT INTO team VALUES (‘FER’,’Ferrari’,’History’);

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IOT OverflowExample Index Block


Row#0[8013] flag: K----, lock: 2col 0; len 3; (3): 46 45 52tl: 17 fb: --H-F-– lb: 0x0 cc: 1nrid: 0x010000ea.0col 0: [ 7]Dump of memory from 0x04B92FB9 to 0x04B92FC04B92FB0 72654607 69726172 [.Ferrari]

04 02 03 46 45 52 28 00 01 01 00 00 EA 00 00 07 46 65 72 72 61 72 69

Index Row Header

Index Col 0

Table Row Header

Pointer to Overflow

Table Col 0

Flag Lock Length Lock #Cols LengthROWIDFlag

F E R F e r r a r i

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IOT OverflowExample Overflow Block


tab 0, row 0, @0x1fb1tl: 7 fb: -----L– lb: 0x1 cc: 1col 0: [ 3] 49 54 41

04 01 01 03 49 54 41

Table Row Header

Table Col 0

Lock #Cols LengthFlag

I T A

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IOT OverflowSummary Store frequently accessed columns in index segment Store rarely accessed columns in overflow segments

Overflow segments Useful for variable length columns e.g Useful for nullable columns May reduce index height May increase row density

Statements accessing overflow segments must access index segment first require additional logical I/Os

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IOT Secondary IndexesIntroduction Introduced in Oracle 8.1.5

Allow additional B*tree indexes to be created on IOTs Allow new access paths

Can be created on Primary key columns Non key columns Overflow columns

Can be compressed Can be partitioned Cannot be reversed

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IOT Secondary IndexesExecution Plans

CREATE TABLE team(

team_key VARCHAR2(3),team_name VARCHAR2(50),country_key VARCHAR2(3),CONSTRAINT team_pkPRIMARY KEY (team_key)


SELECT team_key,team_name FROM teamWHERE country_key = ‘ITA’;

CREATE INDEX team_countryON team (country_key);

0 SELECT STATEMENT1 0 INDEX (UNIQUE SCAN) OF ‘TEAM_PK’2 1 INDEX (RANGE_SCAN) OF ‘TEAM_COUNTRY’;

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IOT Secondary IndexesRow Structure Each secondary index row contains

key values physical ROWID guess primary key

Not the same as UROWIDs

As insertions occur IOT rows can move to different blocks Physical ROWID guesses are not updated in secondary index Guesses degrade over time

Percentage of rows with valid guesses is collected by ANALYZE and DBMS_STATS and recorded in

DBA_INDEXES.PCT_DIRECT_ACCESS

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IOT Secondary IndexesExample Leaf Row

row#0[8018] flag: K----, lock: 2col 0; len 3; (3): 49 54 41col 1; len 3; (3): 46 45 52tl: 8 fb: --H-FL– lb: 0x0 cc: 1col 0: [ 4]Dump of memory from 0x05B12FBC to 0x05B12FC05B12FB0 EA010001

04 02 03 49 54 41 03 46 45 52 2C 00 01 04 01 00 01 EA

Index Row Header

Index Col 0

Table Row Header

Pointer to IOT Block

Index Col 1

Flag Lock Length Lock #Cols LengthFlagLength


I T A F E R

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IOT Mapping TablesIntroduction Introduced in Oracle 9.2.0 Required to support IOT bitmap secondary indexes IOT rows subject to block splits

Can move from block to block Bitmap indexes rows reference contiguous set of slots

IOT must be created with MAPPING TABLE clause

Bitmap index stores mapping table blocks Read access via IOT bitmap secondary indexes as follows

Obtain mapping table block number from bitmap index Obtain primary key from mapping table block Use primary key to access IOT

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IOT Mapping TablesSegments IOT Mapping Table segments are created automatically when

MAPPING TABLE clause is used

Segment name is

Where object_id is the object id of the IOT / IOT partition

Mapping table contains one column

SYS_IOT_MAP_<object_id>

Column Name Column Type

SYS_NC_01 UROWID (Type 208)

SYS_IOT_MAP_6650

e.g.

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IOT Mapping TablesExecution Plan

CREATE TABLE team(

team_key VARCHAR2(3),team_name VARCHAR2(50),country_key VARCHAR2(3),CONSTRAINT team_pkPRIMARY KEY (team_key)

)ORGANIZATION INDEXMAPPING TABLE;

CREATE BITMAP INDEX team_countryON team (country_key);

SELECT team_key,team_name FROM teamWHERE country_key = ‘ITA’;

0 SELECT STATEMENT1 0 INDEX (UNIQUE SCAN) OF ‘SYS_IOT_TOP_6650’2 1 BITMAP CONVERSION (TO ROWIDS)3 2 BITMAP INDEX (SINGLE VALUE) OF ‘TEAM_COUNTRY’;

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IOT Mapping TablesExample Bitmap Index Leaf Block

Row#0[8013] flag: -----, lock 0Col 0: len 3; (3): 49 54 41Col 1: len 6; (6): 01 00 0a 62 00 00Col 2: len 6; (6): 01 00 0a 62 00 07Col 3: len 1; (2): 00


00 00 03 49 54 41 06 01 00 0A 62 00 00 06 01 00 0A 62 00 07 01 00

LengthFlag Lock Length Length Length

Index Row Header

Start ROWID

End ROWID

Index KeyColumn

Bitmap

Start ROWID and end ROWID refer to blocks in mapping table

I T A

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IOT Mapping TablesExample Mapping Table Block

tab 0, row 0, @0x1f91tl: 15 fb: --H—FL- lb: 0x1 cc:1col 0: [11] 02 04 00 00 00 00 03 46 45 52 FE

0B 02 04 00 00 00 00 03 46 45 52 FE

Index Col 0

Block Pointer ?

TerminatorLength Length#Cols Length


2C 01 01 0B 02 04 00 00 00 00 03 46 45 52 FE

Flag Lock #Cols

Table Row Header

UROWID

F E R

F E R

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IOT Mapping IndexesExample IOT Block


04 02 01 00 0A 62 00 00 03 46 45 52 2C 00 02 07 46 65 72 72 61 72 69 03 49 54 41

Row#0[8009] flag: K----, lock: 2, data:(6) 01 00 0a 62 00 00col 0; len 3; (3): 46 45 52tl: 15 fb: --H-FL– lb: 0x0 cc: 2col 0: [ 7]Dump of memory from 0x05C92FB5 to 0x05C92FBC5C92FB0 72654607 69726172 [.Ferrari]col 1: [ 3]Dump of memory from 0x05C92FBD to 0x05C92FC05C92FB0 41544903 [.ITA]


Index Row Header

MappingTable

ROWID

Table Row Header

Table Col 0

Table Col 1

Index Col 0

F E R I T AF e r r a r i

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IOT Mapping TablesSummary Bitmap indexes can be much more efficient than B*Tree

indexes requiring Less physical storage Fewer logical I/Os

Mapping tables require Additional physical disk usage Additional logical I/Os for SELECT and DML

Each IOT leaf row requires additional six bytes for mapping table ROWID

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Thank you for your interest

For more information and to provide feedback

please contact me

My e-mail address is:[email protected]

My website address is:

www.juliandyke.com

1 IOT Internals Julian Dyke Independent Consultant Web Version juliandyke.com © 2005 Julian Dyke.

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