1. 1 DynaMat A Dynamic View Management System for Data Warehouses Vicky :: Cao Hui Ping Sherman :: Chow Sze Ming CTH :: Chong Tsz Ho Ronald :: Woo Lok Yan Ken :: Yiu Man Lung

2. 2 Outline Introduction Background DynaMat Experiments Conclusions References

3. 3 Introduction On-Line Analytical Processing (OLAP)  Why OLAP? A dominant factor for Support Decision Application  Ad-hoc data-intensive queries  Costly multi-joins and aggregations Materialized View  Why materialize view? Data amount in data warehouses is very big OLAP query is very complex and costly OLAP query result maybe summary data  Represent a set of redundant entities in a data warehouse that are used to accelerate OLAP.

4. 4 Introduction(cont.) Basic rule to materialize view  Given some space restriction, select some suitable views to materialize. Data warehouse Materialized View Query Not all data redundant ? How many? Which?

5. 5 Background Research topics on materialized view  Store summary data as materialized view  Efficiently compute and update views Static selection of views  Pre-determine which view should be materialized and materialize them before the queries come Static!

6. 6 Background(cont.) Limitations of Static Selection of Views  Many queries can’t be answered by the materialized data since query patterns change  Update is costly as data is changing overtime  Administrator: Monitor query patterns Re-calibrate such views by rerunning the query Automated view selection  Dynamic View Management: DynaMat workload heavy!!!

7. 7 DynaMat Charactmaeristics:  Dynamically materializes information at different granularity  View Selection + View maintenance in a single framework System overview View pool organization Directory index Query execution Pool maintenance

8. 8 System Overview Components Two phrases  On-line Query  Off-line Update Store materialized data Support sub-linear search in V Whether the materialized data can be used to answer query? Off-line update Maintain View Pool 1 2 3.2 4.2 3.1 4.1 S

9. 9 View Pool Organization Multi-Range query(MRQ)  Hyper-plane: n-vector  n: number of group by attributes  Ri: full range of the domain; single value; empty range Select product, year, sum(sales) From F Where product=‘p1’ Group by product, year F (product, country, year, sales) Product(p1, p35) Country (c1, c30) Year (1995,2000)

10. 10 View Pool Organization(cont.) MRF(Multidimensional Range Fragments)  Each fragment can also be represented by a hyper-plane  Basic logical unit in the pool Many fragments in the View Pool ProductyearCountrySales P11997C130 P11997C250 P11999C140 P11999C360 P21997C140 P21998C250 P21998C330 F ProductyearCountrySales P11997All80 P11999All100 MRF

11. 11 Directory Index Facilitate the search in view pool Directory index is a R-tree based on fragment’s hyper-planes. Each fragment corresponds to one entity in directory index Year P1 19952000 Product P15 P10 1997 Directory Index

12. 12 Query Execution Query Step:  From MR query, get its hyper-plane  Query the view pool based on the directory index Year P1 19952000 Product P15 P10 1997 Directory Index f2 f3

13. 13 Query Execution(cont.) Query cases:  One fragment f matches the query exactly Retrieve f and return it back to the user  No exact match, but many fragments can be used to answer the query Choose the best fragment to answer the query  The query can not be answered by the view pool Perform the query directly on the DW Query results  ACE in the later two cases

14. 14 Pool Maintenance Admission Control Entity(ACE) Two cases to maintenance  New query results come  Data in base relation changes Space Bound &Time Bound  Space bound: View pool hits the pre-defined space window W space  replace  Time bound: the system restrict the time window W time to refresh the fragments. Goodness measure to determine whether a fragment is good enough.

15. 15 Pool Maintenance(cont.) Pool maintenance during queries  New query results can be stored in the view pool if it has enough space  Call replace algorithm if it hits the space constraint. If goodness(new result) >goodness( f victim ), E vict f victim, This process doesn’t stop until there is enough space for the new query result. Maintenance of the father pointers evicted f victim f new : new query result Goodness(f victim )< goodness(f new ) f1 f2

16. 16 Pool Maintenance(cont.) Pool maintenance during updates  Condition:data in base relation changes  Step: For each fragment compute minimum update cost UC(f)  Get all necessary deltas, which make change to the DW  Get from the directory index  Calculate dV and update each f by querying dV Total update cost: Evict fragments from the view pool according to the non-ascending order of their cost, if the UC(V) is greater than the time bound ProductyearCountrySales P301999C130 P12000C250 P41999C140 P11999C660 ProductyearCountrySales P301999C130 P41999C140 P12000C250 P11999C660 dV ={(p1,p35)},(1995,2000),(c1,C10)} Delta

17. 17 Pool Maintenance(cont.) Year P1 19952000 Product P15 P10 1997 ProductyearCountrySales P301999C130 P12000C250 P41999C140 P11999C660 ProductyearCountrySales P41999C140 P12000C250 P11999C660 dV ={(p1,p20)},(1995,2000),(c1,C10)} Delta

18. 18 Experiments Measure: Detailed Cost Savings Ratio  Ci: Cost of answering queries in DW  Si: Saving cost when answering queries in view pool   The greater the DCSR, the better the performance

19. 19 Experiments(cont.) Comparison with the optimal static view selection  1 Fact table: 6 dims, 20 million records  updates: 40 sets * 100 thousand records  Time constraint: 2% of the full Data Cube  Queries: 40 sets*500 MR Queries.

20. 20 Conclusion DynaMat: A view management system  Dynamically materializes results from incoming queries  Exploits them to future use  Considering time and space constraint  Better performance than static methods

21. 21 Reference Y. Kotidis, N. Roussopoulos. DynaMat: A Dynamic View Management System for Data Warehouses. In Proceedings of ACM SIGMOD International Conference on Management of Data, 371-382, Philadelphia, Pennsylvania, June 1999. Y. Kotidis, N. Roussopoulos. A Case for Dynamic View Management. ACM Transactions on Database Systems, Volume 26(4), 388-423, 2001. Original presentation by the author, http://www.cs.umd.edu/~kotidis/Publications/Sigmod99

22. 22 Thanks! Q&A?