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SQL Explore 2012 - Michael Zilberstein: ColumnStore
- 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
- 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