1. Boosting
performance
with
Columnstore
Indexes
Michael
Zilberstein
DBArt Ltd
Michael@dbart.co.il

2. DEMO

3. History
• Column-oriented databases:
– Sybase IQ
– Vertica
– Aster Data
– Greenplum
–…
• Excel PowerPivot.
• VertiPaq.
• xVelocity Columnstore index.

4. C1 C2 C3 C4 C5 C6
Uses VertiPaq
compression

5. Reduced IO
Fetches only needed columns
from disk
SELECT C2, SUM (C3) …
C2 C3 Columns are compressed
C1 C4 C5 C6
Less IO
Better buffer hit rates

6. New query execution technology
• Batch mode execution of some operations
– processes rows in batches
– groups of batch operations in query plan
• Better parallelism, better algorithms

7. Dictionary-based compression
Year of Code
Birth
1996 1 Internal Dictionary
1975 15
Year of
1948 50
Birth
1932 58 On-the-fly build dictionary
1996 … 60
with all distinct value.
1975 Substitute non-selective
values with ID.
1975 Index in our example – 6
bits per row.
1948 Year of
Birth
1932 Code
1 Compressed Fact
…
15
15
50
58
60

8. Segments
C1 C2 C3 C4 C5 C6 Column segment
Set of about contains values from
1M rows one column for a set
of about 1M rows
Column segments
are compressed
Each column
segment stored in
separate LOB
Column segment is
Column unit of transfer from
Segment disk

9. Data Dictionary Views

10. New execution plan elements

11. Best practices / worst practices
• Best practices:
– Put columnstore indexes on large tables only.
– Include every column of the table in the columnstore
index.
– Structure your queries as star joins with grouping and
aggregation as much as possible.
• Worst practices:
– Avoid JOIN and/or filter on string columns in the table
with columnstore index.
– Avoid OUTER JOIN, UNION ALL, IN/NOT IN.
– Avoid JOIN between 2 Fact tables.

12. Datatype Limitations
• Decimal > 18 digits
• (Var)Binary
• BLOB
• (N)Varchar(max)
• Uniqueidentifier
• Date/Time types > 8 bytes (Datetime2 etc)
• CLR

13. Issues and Workarounds: good, bad and ugly
• Outer Joins
• NOT IN
• Scalar Aggregates
• Multiple DISTINCT
• UNION ALL
• IN and EXISTS

14. Data loading and columnstore index
• Columnstore index makes table read-only.
DEMO

15. Data loading and columnstore index
• 2 ways to load data:
– Partition switching
– Disable/drop index -> load data ->
create/rebuild index.

16. References
• http://channel9.msdn.com/Events/TechEd/Nor
thAmerica/2011/DBI312
• http://social.technet.microsoft.com/wiki/cont
ents/articles/4995.sql-server-columnstore-
performance-tuning.aspx

17. Q&A
Michael Zilberstein
Tel: 052-4767219
E-Mail: Michael@dbart.co.il