1. Inside of SQL Server Indexes

2. Slava Murygin
@SlavaSQL
SlavaSQL.BLOGSPOT.com

4. This presentation does not cover:
Compressed Indexes
Spatial Indexes
Full-Text Indexes
XML Indexes
In-Memory Indexes

5. SQL Database Structure
Database File
SQL DB
Extent = 8 Pages
Pages 8 16
1 Page = 8 Kb
1 Extent = 64 Kb 24
64 Kb is Standard Memory Block 32

6. Page Structure

7. Table Structure. The Heap.
The Heap: Table without Clustered Index.
Index Allocation Map 1
IAM
Page 2 3 4
. . . N
N+1
N+2
Data Pages

14. Why do we need Indexes To reduce number of IO during data extraction
Support sorting operations
Establish uniqueness within a column or set of columns
Indexes: Exchange Money Disk Space for Time.

15. Index B-Tree Structure
Root
Page
Intermediate Pages
Leaf Pages

16. Two Classes of indexes:
Clustered Indexes
Can be only one per table (and must be unique)
Non-Clustered Indexes
Can be multiple of different types
Both can be Unique and/or Composite

17. Next page Previous Page
Clustered Index
AAA
BAA
CAA
Root Page
AAA
ABA
ACA
BAA
BBA
BCA
Intermediate Pages
CAA
CBA
CCA
Next page Previous Page
AAA
AAB
AAC
ABA
ABB
ABB+8
ACA
ACB
ACC
BAA
BAB
BAC
BBA
BBB
BBC
BCA
BCB
BCC
CAA
CAB
CAC
CBA
CBB
CBC
CCA
CCB
CCC
Leaf Pages = Data Pages

18. Clustered Index - Details
Clustered Index keep uniqueness or build it if it does not exist, which requires extra space on all levels.
Leaf Level of Clustered Index IS actual Data.
When we build Clustered Index we copy whole data set to a new place.
Recommendations for Clustered Index:
- Start from most used and diverse columns;
- Cover the most expensive queries;
- Keep Clustered Index as short as possible.

27. Page Splits Updating variable sized columns
Inserting records within a range
AAA-X
ABA-Y
ACA-Z
INSERT
“ABBC”
AAA-X
ABA-Y1
ABBC-Y2
ACA-Z X
AAA
AAB
AAC Y
ABA
ABB
ABC Z
ACA
ACB
ACC X
AAA
AAB
AAC Y1
ABA
ABB Y2
ABBC
ABC Z
ACA
ACB
ACC

29. Fill Factor and PAD_INDEX
AAA
AAC
ABB
ACA
AAA
AAB
AAC
ABA
ABB
ABC
ACA
ACB
Fill Factor: Exchange Space for Time

31. Non-Clustered Indexes
Regular Non-Clustered Index:
- Filtered;
- Covering;
- With Included
Columns;
Indexed Views (materialized views)
Special Indexes:
- Spatial;
- Compressed;
- XML;
- Full-Text;
- In-Memory;
- Columnstore;

32. Non-Clustered Indexes at Work
Use Clustered index to retrieve a data
If there is no Clustered index
they address data directly

42. Covering Indexes Space for Time
Do not require to go to a data Level or Clustered Index

48. Indexes with Included Columns
Reduce Index size
Help to avoid some Index limits

49. Filtered Indexes
Reduce Index size

51. Querions?
@SlavaSQL
SlavaSQL.BLOGSPOT.com