The document provides an overview of Oracle indexes from a conceptual and internal perspective. It discusses B-tree indexes, including their structure, leaf and branch nodes, and how select, update, delete and insert operations are handled internally. It also covers bitmap indexes and their storage format, as well as function-based and reversed indexes.

1. Oracle Indexes: From the Concept to Internals
Prepared by:
Deiby Gómez
Oracle ACE & OCM 11g
Pythian Oracle Consultant
Session ID#: 292

2. © 2014 Pythian Confidential2
- Oracle ACE (23 years old)
- Oracle Certified Master 11g (24 years old)
- OCP 11g & 12c, RAC 11g, SOA, Exadata X3
- President of Guatemala Oracle User Group
- Pythian Oracle Database Consultant
Twitter: @hdeiby
Facebook: /HDeiby
Email: gomez@pythian.com
Blog: www.oraclefromguatemala.com.gt

3. © 2014 Pythian Confidential3
WHAT IS AN “INDEX”?

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B-TREE INDEXES

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Root (Branch)
Branch
Leaf
B-TREE INDEX: CONCEPTS

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WHAT IS AN “INDEX”?

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B-TREE INDEX: INTERNALS
Header
Free Space
Data

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B-TREE INDEX: INTERNALS
Leaf node Branch node
Branch block dump
=================
header address 139950945835596=0x7f48de699a4c
kdxcolev 2
KDXCOLEV Flags = - - -
kdxcolok 0
kdxcoopc 0x80: opcode=0: iot flags=--- is
converted=Y
kdxconco 1
kdxcosdc 0
kdxconro 1
kdxcofbo 30=0x1e
kdxcofeo 8048=0x1f70
kdxcoavs 8018
kdxbrlmc 16779590=0x1000946
kdxbrsno 0
kdxbrbksz 8056
kdxbr2urrc 0
Leaf block dump
===============
header address 139950941831268=0x7f48de2c8064
kdxcolev 0
KDXCOLEV Flags = - - -
kdxcolok 0
kdxcoopc 0x80: opcode=0: iot flags=--- is
converted=Y
kdxconco 1
kdxcosdc 0
kdxconro 1
kdxcofbo 38=0x26
kdxcofeo 8021=0x1f55
kdxcoavs 7983
kdxlespl 0
kdxlende 0
kdxlenxt 0=0x0
kdxleprv 0=0x0
kdxledsz 6
kdxlebksz 8032
row#0[8021] flag: ------, lock: 0, len=11, data:(6):
01 00 00 85 00 00
col 0; len 2; (2): c1 02
----- end of leaf block dump -----
row#0[8048] dba: 16779592=0x1000948
col 0; len 3; (3): c2 09 10
----- end of branch block dump -----

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B-TREE INDEX: INTERNALS
Leaf node Branch node
Branch block dump
=================
header address 139950945835596=0x7f48de699a4c
kdxcolev 2
KDXCOLEV Flags = - - -
kdxcolok 0
kdxcoopc 0x80: opcode=0: iot flags=--- is
converted=Y
kdxconco 1
kdxcosdc 0
kdxconro 1
kdxcofbo 30=0x1e
kdxcofeo 8048=0x1f70
kdxcoavs 8018
kdxbrlmc 16779590=0x1000946<--Address to Prev
Node
kdxbrsno 0<--Last index entry modified
kdxbrbksz 8056<--usable space in the block.
kdxbr2urrc 0
row#0[8048] dba: 16779592=0x1000948 <--Pointer
to the 2nd intermediate branch block
col 0; len 3; (3): c2 09 10 <--first column
value used to navigate
----- end of branch block dump -----
Leaf block dump
===============
header address 139950941831268=0x7f48de2c8064
kdxcolev 0 <--block level
KDXCOLEV Flags = - - -
kdxcolok 0 <--itl of service tx holding block lock
kdxcoopc 0x80: opcode=0: iot flags=--- is converted=Y
<--block lock op code
kdxconco 1<--number of columns
kdxcosdc 0<--Split or Deleted count
kdxconro 1<--Number of entries
kdxcofbo 38=0x26 <--offset where the free space in
this block starts
kdxcofeo 8021=0x1f55 <--offset where the free space
in this block finishes
kdxcoavs 7983 <--(kdxcofeo-kdxcofbo) The free space!
kdxlespl 0<--space held by unlocked split entries
kdxlende 0 <--entries deleted
kdxlenxt 0=0x0 <--there is not pointer to Next Leaf
Node
kdxleprv 0=0x0 <--there is not pointer to Previous
Leaf Node
kdxledsz 6<--bytes used by rowed data (KEYDATA)
kdxlebksz 8032<--usable space in the block.
row#0[8021] flag: ------, lock: 0, len=11, data:(6):
01 00 00 85 00 00
col 0; len 2; (2): c1 02
----- end of leaf block dump -----

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B-TREE INDEX SELECT OPERATION: CONCEPTS
1,rowid
1,rowid 2,rowid
1,rowid 2,rowid …. 814,rowid 815,rowid
create table dgomez.t1(id number,value varchar2(20));
Select id,value from dgomez.t1 where id=2;
1,rowid 2,rowid …… 814,rowid 815,rowid
ID Value
2 Deiby
Note: 1 entry per Leaf Node

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B-TREE INDEX SELECT OPERATION: INTERNALS
SQL> select id, value from dgomez.t1 where id=2;
ID V
---------- -
2 Deiby
Execution Plan
----------------------------------------------------------
Plan hash value: 408250987
-----------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 15 | 2 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| T1 | 1 | 15 | 2 (0)| 00:00:01 |
|* 2 | INDEX UNIQUE SCAN | BTREE | 1 | | 2 (0)| 00:00:01 |
-----------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("ID"=2)
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
4 consistent gets
0 physical reads
0 redo size
457 bytes sent via SQL*Net to client
508 bytes received via SQL*Net from client
1 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
SQL>

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B-TREE INDEX DELETE OPERATION: INTERNALS
Delete from ioug.t1 where vkey='D';
row#0[8021] flag: ------, lock: 0, len=11
col 0; len 1; (1): 41
col 1; len 6; (6): 01 80 00 87 00 00
row#1[8010] flag: ------, lock: 0, len=11
col 0; len 1; (1): 42
col 1; len 6; (6): 01 80 00 87 00 01
row#2[7977] flag: ------, lock: 0, len=11
col 0; len 1; (1): 43
col 1; len 6; (6): 01 80 00 87 00 03
row#3[7988] flag: ---D--, lock: 2, len=11
col 0; len 1; (1): 44 <---vkey=’D’
col 1; len 6; (6): 01 80 00 87 00 02
----- end of leaf block dump -----v
• The entry is just marked as “deleted” but it is not
deleted really.
• The deleted Index entry can be reused.

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B-TREE INDEX UPDATE OPERATION: INTERNALS
row#0[8021] flag: ------, lock: 0, len=11
col 0; len 1; (1): 41
col 1; len 6; (6): 01 80 00 87 00 00
row#1[8010] flag: ------, lock: 0, len=11
col 0; len 1; (1): 42
col 1; len 6; (6): 01 80 00 87 00 01
row#2[7999] flag: ---D--, lock: 2, len=11
col 0; len 1; (1): 43 <---vkey=’C’
col 1; len 6; (6): 01 80 00 87 00 02
row#3[7988] flag: ------, lock: 2, len=11
col 0; len 1; (1): 44 <---vkey=’D’
col 1; len 6; (6): 01 80 00 87 00 02
----- end of leaf block dump -----
update ioug.t1 set vvalue=‘D' where vkey='C';

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BITMAP INDEXES

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BITMAP INDEX: CONCEPTS
15

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BITMAP INDEX: CONCEPTS

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BITMAP INDEX SELECT OPERATION
17

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BITMAP INDEX UPDATE OPERATION
18
row#0[8005] flag: ------, lock: 0, len=27
col 0; len 6; (6): 43 61 6e 61 64 61
col 1; len 6; (6): 01 80 00 83 00 00
col 2; len 6; (6): 01 80 00 83 00 0f
col 3; len 3; (3): c9 0c 03
row#1[7886] flag: ------, lock: 2, len=35
col 0; len 9; (9): 47 55 41 54 45 4d 41 4c 41vkey=GUATEMALA
col 1; len 6; (6): 00 00 00 00 00 00 Beginning of ROWIDs
col 2; len 6; (6): 01 80 00 83 00 0f Ending of ROWIDs
col 3; len 8; (8): f9 91 df 80 dc 08 61 08 Bitmap String
row#2[7975] flag: ---D--, lock: 2, len=30
col 0; len 9; (9): 47 75 61 74 65 6d 61 6c 61vkey=Guatemala
col 1; len 6; (6): 01 80 00 83 00 00 Beginning of ROWIDs
col 2; len 6; (6): 01 80 00 83 00 0f Ending of ROWIDs
col 3; len 3; (3): c9 61 08 Bitmap String
row#3[7948] flag: ------, lock: 0, len=27
col 0; len 6; (6): 4d 65 78 69 63 6f
col 1; len 6; (6): 01 80 00 83 00 00
col 2; len 6; (6): 01 80 00 83 00 0f
col 3; len 3; (3): c9 92 04
----- end of leaf block dump -----
update ioug.t1 set vkey='GUATEMALA' where vkey='Guatemala';

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BITMAP INDEX INSERT OPERATION
• If the KEY exists:
– The Bitmap String is updated
• If the KEY doesn’t exist
– A new Bitmap Entry is created with its
own Bitmap String
19

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BITMAP INDEX DELETE OPERATION
• If after the deletion there are some rows with the KEY afer
the DELETE operation, then the Index is not marked as
deleted and only the Bitmap String is updated with “0” in
the positions where our deleted rows were stored.
• If after delete there is no any row with the KEY after the
DELETE operatioN, then the Index Entry is marked as
deleted with “--D--”
20
row#2[7975] flag: ---D--, lock: 2, len=30
Before-->
Delete Op-->
After-->
Before-->
After-->

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FUNCTION-BASED INDEXES

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FUNCTION-BASED INDEX
22
create index functionbasedIDX on dgomez(upper(value));
insert into dgomez values (1,'deiby');
Leaf block dump
===============
…..
…..
row#0[8017] flag: ------, lock: 0, len=15
col 0; len 5; (5): 44 45 49 42 59 ’DEIBY’(not ‘deiby’)
col 1; len 6; (6): 01 40 00 83 00 00
----- end of leaf block dump -----
• The same B-Tree structure and
• The same behavior than B-Tree Indexes but
with the values stored with the function applied.

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REVERSED-KEY INDEXES

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REVERSED-KEY INDEX
24
• The same B-Tree structure and
• Every byte of the KEY is reversed .
create index reversekeyIDX on dgomez(value) reverse;
• 204
• 205
• 206
• 207
• 402
• 502
• 602
• 702

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REVERSED-KEY INDEX
25
• The same B-Tree structure and
• Every byte of the KEY is reversed .
create index reversekeyIDX on dgomez(value) reverse;
row#0[8019] flag: ------, lock: 0, len=13
col 0; len 3; (3): 34 30 32<-The value
col 1; len 6; (6): 02 40 00 87 00 04<-RowID
row#1[8006] flag: ------, lock: 0, len=13
col 0; len 3; (3): 35 30 32
col 1; len 6; (6): 02 40 00 87 00 05
row#2[7993] flag: ------, lock: 0, len=13
col 0; len 3; (3): 36 30 32
col 1; len 6; (6): 02 40 00 87 00 06
row#3[7980] flag: ------, lock: 0, len=13
col 0; len 3; (3): 37 30 32
col 1; len 6; (6): 02 40 00 87 00 07
----- end of leaf block dump -----
34 30 32 => 4 0 2
35 30 32 => 5 0 2
36 30 32 => 6 0 2
37 30 32 => 7 0 2
But not…
204
205
206
207

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INDEXES ON VIRTUAL COLUMNS

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INDEXES ON VIRTUAL COLUMNS
27
create table dgomez(
value1 varchar(10),
value2 varchar2(10),
result as (value1||value2));
row#0[8017] flag: ------, lock: 0, len=15
col 0; len 5; (5): 64 65 69 62 79 <--deiby
col 1; len 6; (6): 01 40 00 87 00 00 <---ROWID
----- end of leaf block dump -----
create index vcolumn on dgomez(result);
insert into dgomez (value1,value2) values ('dei','by');
• The same B-Tree structure
• The dynamic value of KEY is stored physically.
• A change on dependent column will update the Index

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