Introduction to Columnstore Indexes

Jason
Strate
e: jstrate@pragmaticworks.com
e: jasonstrate@gmail.com
b: www.jasonstrate.com
t: StrateSQL
Resources jasonstrate.com/go/indexing
Introduction
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Agenda
Introduction Columnstore Basics
SQL Server
Columnstore
Non-Clustered
Columnstore
Clustered
Columnstore
Summary

Session Goals
• Identify differences between rowstore and
columnstore indexes
• Describe implementation of columnstore index
in SQL Server
• Define pros and cons with columnstore indexes
• Demonstrate use of columnstore indexes

Index Problems
• Indexes traditionally are row-based
– All columns for row stored together
• Any column read brings over all columns
– Impacts IO, CPU, and memory
– Typically 15% of DW columns in queries
• Databases growing 10x every 5 years
• Tuning for over indexing, under indexing, and
bookmark lookups

Columnstore Basics
• Change data storage from row to column
based
– Rowstores
– Columnstores
• Data grouped by columns
– One column per grouping (segment)
– Data access at columns level
– Only return columns required for query

Say
What?!

Traditional Index

Columnstore Index

Why Columnstore?
• Improved query performance
– Column centric reads
– Heavy data compression
– Processing by batch versus row
• Improved resource utilization
– Smaller index space
– Less memory required

SQL Server Columnstore
• Introduced to improve data warehouse
performance
• Available since SQL Server 2012
• SQL Server 2012
– Non-clustered columnstore
• SQL Server 2014
– Clustered columnstore

Columnstore Attributes
• Introduced in SQL Server 2012
• Supports batch mode processing
• SQL Server 2012
– Non-clustered columnstore
– No key columns
– Support partitioning
– Read only index
• SQL Server 2014
– Clustered columnstore
– Columnstore archive format
– Readwrite when clustered

Batch-mode Processing
1 record versus 415 records

Columnstore Restrictions
• Cannot be a unique index.
• Cannot be created on a view or
indexed view.
• Cannot include a sparse
column.
• Cannot act as a primary key or
a foreign key.
• Cannot be created with
the INCLUDE keyword
• Cannot include
the ASC or DESC keywords for
sorting the index
• No seek operations
• Cannot contain a column with a
FILESTREAM attribute
• Limited data types
– Except varchar(max),
nvarchar(max), binary,
varbinary, ntext, text, image,
uniqueidentifier, rowversion,
timestamp, sqlvariant, xml, CLR
types
• Feature restrictions
– Replication
– Change tracking
– Change data capture
– Filestream

Non-Clustered Columnstore
• Available in:
– SQL Server 2012
– SQL Server 2012 Parallel Data Warehouse
– SQL Server 2014
• One non-clustered columnstore per table
– Support tables heap or clustered index
• Add in all columns from table
– No key columns
• Best support star-join style queries
• Avoid OUTER JOIN and NOT IN
– Prevent batch processing

Updating Non-Clustered Columnstore
• Drop the columnstore
• Perform DML
• Recreate columnstore
Drop and
Rebuild
• Create new partition with modified data
• Create columnstore
• Switch in partition
Partition
Switch
• Apply changes to separate table
• UNION ALL columnstore or change table
• Manage DML through trigger
Partitioned
View

NON-CLUSTERED COLUMNSTORE
Demo

Clustered Columnstore
• Available in:
– SQL Server 2012 Parallel Data Warehouse
– SQL Server 2014
• One clustered columnstore per table
– Is primary storage for data
– Reduces space requirements
• Can leverage columnstore archive format
• Same design patterns as non-clustered
• Preferred over non-clustered columnstore

CLUSTERED COLUMNSTORE
Demo

Summary
• Columnstore indexes change data can be
accessed
• Provides increased data compression
• Retrieves only the columns that are needed
• Primary benefit in data warehouses
– Slowly or unchanging data

More Information
Expert Performance Indexing
For SQL Server 2012
Jason Strate
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Name: Jason Strate
Email: jstrate@pragmaticworks.com
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Introduction to Columnstore Indexes

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