1. Data Warehousing Seminar Chapter 13 Indexing the Warehouse
M.S. 2
Hyeyoung Cho

2. Oracle Storage Database Tablespace Data file Logical Physical Segment
Extent
OS block
Oracle block

3. Data block and Row Data block Row header Free space Data Row header
Column length
Column value

4. What Is an Index? A structure separate from the table
Stores the location of rows based on the specified column values
Speed up the retrieval of rows by using a pointer
Reduce disk I/O by using rapid path access method to locate the data quickly
Used and maintained automatically by the Oracle Server

5. When to create an Index? The table is large
The columns are often used as a condition in the query
The column contains a wide range of value or a large number of null value
Most queries expected to retrieve less than 5% of the rows
Automatically created when define PRIMARY KEY or UNIQUE constraint

6. Classification of Indexes
Logical(application perspective)
Single column or concatenated
Unique or nonunique
Function-based
Physical(storing perspective)
B-tree
Normal or reverse key
Bitmap
Partitioned or nonpartitioned

7. Single-column and Composite index
Single-column indexes
one column in the index key
Composite index
multiple columns in the index key
Max : 32 , 1/3 of the data block size
create index purchase1 on purchase (purchase_id)
storage (initial 2m next 2m pctincrease 0) tablespace purch_ind1;
create index purchase1 on purchase (purchase_id, purchase_date, total_amt)
storage (initial 2m next 2m pctincrease 0) tablespace purch_ind1;

8. Unique or nonunique Unique Nonunique
A single key point to only one row
Nonunique
A single key associated with multiple rows

9. Function-based indexes(1/3)
Oracle 8i new feature
Query rewrite privilege required
Using functions or expressions involve one or more columns in the table
Precomputes the value of the function or expression store it in the index
Created as either a B-tree or a Bitmap index

10. Function-based indexes(2/3)
Example1. Client names in a mixed case
Index creation
Statement predicate
create index billing_upcl on billing (upper(client))
storage(initial 20m next 80m maxextents unlimited pctincrease 0)
tablespace my_indexes;
select bill_id, client, state_nm from billing
where upper(client) = ‘MONSANTO’ ;

11. Function-based indexes(3/3)
Example2. Commission exceeded 25% of salary for the certain time period
Index creation
Statement predicate
create index sale_bc_amt on sale (comm/(base+comm)*100) …
storage(initial 20m next 80m maxextents unlimited pctincrease 0)
tablespace my_indexes;
select sum(comm) from sale
where comm/(base+comm) * 100 > 25
and tr_date between to_date(’01-MAY-2002’, ‘DD-MON-YYYY’)
and to_date (’30-JUN-2002’, ‘DD-MON-YYYY’);

12. B-tree indexes(1/3) Traditional indexing technique!
Stores a list of ROWID for each key
A hierarchy of highest-level and lower level index blocks(root> branch> leaf)
Leaf Entry Format
Header : chaining info, row lock status, number of columns
Key column length and value pairs
ROWID : the key values (block num. row num. file num)
Simplicity, Easy maintenance,High cardinality columns
Suitable for exact match query and range query S

13. B-tree indexes(2/3) Structure Root block Branch block Branch block
Leaf blocks
Leaf blocks
Leaf blocks
Index entry header
Key column length
Key column value
ROWID
Index entry

14. B-tree indexes(3/3) Creating Normal B-Tree Indexes
Create index employee_last_name_idx on employee(last_name)
pctfree 30 storage (initial 200k next 200k pctincrease 0 maxextents 50)
tablespace indx;
Create [UNIQUE] index [schema.] index
on [schema.] table(column [ASC | DESC] [, column [ASC | DESC] ] … )
[TABLESPACE tablespace]
[PCTFREE integer] [INITRANS integer] [MAXTRANS integer]
[storage – clause]
[LOGGING | NOLOGGING] [NOSORT]

15. Reverse Key indexes(1/3)
Reverse the bytes of each column indexed (except the ROWID)
Spreading the work load across multiple blocks
Unsuitable for range queries
Use the keyword reverse

16. Reverse Key indexes(2/3)
Index on EMPLOYEE(ID)
EMPLOYEE table
KEY ROWID
ID (BLOCK# ROW# FILE#) F F F F F
… …
ID FIRST_NAME JOB
7499 ALLEN SALESMAN
7369 SMITH CLERK
7521 WARD SALESMAN
7566 JONES MANAGER
7654 MARTIN SALESMAN
… … …

17. Reverse Key indexes(3/3)
Creating Reverse key index
Create unique index orders_id_idx on orders(id) reverse
pctfree 30 storage (initial 200k next 200k pctincrease 0 maxextents 50)
tablespace indx;
Create [UNIQUE] index [schema.] index
on [schema.] table(column [ASC | DESC] [, column [ASC | DESC] ] … )
[TABLESPACE tablespace]
[PCTFREE integer] [INITRANS integer] [MAXTRANS integer]
[storage – clause]
[LOGGING | NOLOGGING] [NOSORT]
REVERSE

18. Bitmap indexes(1/4) Stores a bitmap for each key value
For Low cardinality columns
Leaf Entry Format
Header : chaining information, row lock status, number of columns
Key column length and value pairs
Start ROWID , End ROWID : the first row and the last row pointed by the bitmap (block num. row num. file num)
Bitmap : a string of bits depending on key value
Create bitmap index person_region on person (region);

19. Bitmap indexes(2/4) Structure File 3 Table Block 10 Block 11 Index
Create bitmap index person_region on person (region);
Key startROWID endROWID Bitmap
<Blue , , >
<Green , , >
<Red , , >
<Yellow , , >

20. Bitmap indexes(3/4) Creating Bitmap index
Create bitmap index person_region on person(region) tablespace indexes_prd
pctfree 30 storage (initial 200k next 200k pctincrease 0 maxextents 50)
tablespace indx;
Create [UNIQUE] BITMAP index [schema.] index
on [schema.] table(column [ASC | DESC] [, column [ASC | DESC] ] … )
[TABLESPACE tablespace]
[PCTFREE integer] [INITRANS integer] [MAXTRANS integer]
[storage – clause]
[LOGGING | NOLOGGING] [NOSORT]

21. Bitmap indexes(4/4) Example : a bitmap index on the PERSON table
RESION Bitmap Index
Row Region NorthBitmap EastBitmap WestBitmap SouthBitmap
North
East
West
West
East
West
South
North

22. B-Tree index VS Bitmap index
Suitable for high-cardinality columns
Row-level locking
Bitmap-segment-level locking
Update on keys relatively inexpensive
Update on keys very expensive
More storage
Less storage
Inefficient for queries using OR predicates
Efficient for queries using OR predicates
Useful for OLPT
Useful for data arehousing

23. B-Tree space VS Bitmap space
Bitmap index use 1/100 of the space of the B-tree index!
Unique Column
Values
Cardinality(%)
B-Tree
Space
Bitmap Space
500,000
50.00
15.29
12.35
100,000
10.00
15.21
5.25
10,000
1.00
14.34
2.99
100
0.01
13.40
1.38 5
< 0.01
0.78
Table with 1,000,000 rows

24. Index-organized tables(IOT)(1/3)
Merge the data and index pieces into the same segment
No duplication of the values for the Key column
Faster key-based access for queries involving exact match and range searches
Must have a primary key
Specify an overflow tablespace name and percentage
Secondary indexes(Oracle 8i new feature)

25. Index-organized tables(IOT)(2/3)
Regular table access
IOT access
Only One scan!
Index
Index
ROWID
Non-key columns
Key columns
Row header
Table

26. Index-organized tables(IOT)(3/3)
Creating Index-organized table
create table sales (
office_cd number(3), qtr_end date, revenue number(10,2), review varchar2(1000)
constraint sales_pk PRIMARY KEY (office_cd, qtr_end))
ORGANIZATION INDEX tablespace indx
PCTTHRESHOLD 20
INCLUDING revenue
OVERFLOW tablespace user_data;

27. Indexes on Partitioned Tables(1/4)
An index in several segments
Spread across many tablespaces
Decreasing contention for index lookup
Increasing manageability and scalability
Used with partitioned tables
Creating Index partition for each table partition

28. Indexes on Partitioned Tables(2/4)
Local index
Partition keys of the index match its underlying table
Global index
Partition keys of the index differ from its underlying table
Prefixed index
Left-most column in a partitioned index matches the left-most column in that index’s partition key.
Nonprefixed index
Left-most column in a partitioned index differ from the left-most column in that index’s partition key.

29. Indexes on Partitioned Tables(3/4)
Creating a local partitioned index
create table rumors( thorn_id number(10), rumor_id number(4), …)
partition by range (rumor_id)
(partition rumors_p001 values less than(41),
partition rumors_p002 values less than(50), …
partition rumors_pmax values less than(maxvalue));
create unique index rumors_u1 on rumors(thorn_id, rumor_id) local
(partition rumors_u1_p001,
partition rumors_u1_p002, …
partition rumors_u1_pmax);

30. Indexes on Partitioned Tables(4/4)
Creating a global partitioned index
create table billing(bill_id number(10), region_id varchar2(3), …)
partition by range (bill_id)
(partition bill_p001 values less than(90000),
partition bill_p002 values less than(130000), …
partition bill_pmax values less than(maxvalue));
create unique index billing_u1 on billing(bill_id) global
partition by range (bill_id)
(partition bill_u1_p001 values less than(100000),
partition bill_u1_p001 values less than(200000), …
partition bill_u1_pmax values less than(maxvalue) );

31. Optimizer Histograms(1/2)
Rule-based optimizer
Uses an set of rules for ranking access path
Syntax- and data dictionary-driven
Cost-based optimizer
Chooses least-cost(resource, time) path
Statistics-driven
analyze table table_name compute statistics;

32. Optimizer Histograms(2/2)
Describe the data distribution of a particular column in more detail
Better predicate selectivity estimate for unevenly distributed data
Bucket : the number of distinctive column value
analyze table table_name compute statistics for table for all Indexed columns size 6;

33. Optimizer Histograms(2/2)

34. Guidelines(1) Use NOLOGGING for large indexes creation
Rebuilding index
Use Different tablespace
Converting a index into a reverse key index
Index build times with and without NOLOGGING
Rows in Table
Indexes
With NOLOGGING
Without NOLOGGING
46,34013 13
57s
3m57s
1,094,8146 6
10m5s
24m36s
4,4013,309 4
27m54s
60m48s
ALTER INDEX orders_region_id_idx REBUILD (REVERSE)
Tablespace indx02 NOLOGGING;

35. Guidelines(2) Temporary workspace Sort space parameter
Create during the life of a create index statement
Dropped after the activity completes
Sort space parameter
SORT_AREA_SIZE
Shared pool parameter
shared_pool_size =

36. SGA(System Global Area)
Oracle Instance
SMON
DBW0
PMON
CKPT
LGWR
Background
processes
Memory
structures
INSTANCE
SGA(System Global Area)
Data buffer
Cache
Redo log
Buffer
Shared pool
Library Cache
Data Dictionary cache
Databae
PGA(Program Global Area)
sort area, cursor state,
session info, stack space
User
process
Server process
sql