Materialized view an overview sciencedirect topics. A sql statement that has sumcountavgdistinct column routed to grouping sets mqt returns wrong rerults in query optimization 2 or 5 and above. Materialized query tables db2 developers guide 5th edition. Db2 for i5os database performance and query optimization. When you enable query optimization, db2 is more restrictive of what you can select in the fullselect for a materialized query table. Create usermaintained mqts with query optimization initially disabled. Pdf file for database performance and query optimization. Otherwise, if there is a change in the db2 object and the optimizer is still using the old access path, it will. Query optimization and performance with db2 11 for zos.
If you create the table initially enabled for query optimization, db2 might rewrite queries to use the empty mqt. Using constraints to improve query optimization ibm knowledge. Working with materialized query tables oracle docs. Recommending materialized views and indexes with ibm db2 design advisor. Usually we recommend customers to rebind their static sql to take advantages of the new optimization enhancements delivered in the new release. In essence, a materialized query table mqt is a table that is defined. Using materialized querytables to speed up queries in db2 udb. Front cover sql performance diagnosis ibm redbooks. This differs from the traditional archiving techniques where data is archived. Within ibm db2 9 viper, we implement query rewrite rules that enable the use of materialized views in the evaluation of queries over xml. The database compares the sql with the fullselect statement that was used to define the mqt. Disable query optimization clause specifies that db2 cannot consider the materialized query table in automatic query rewrite.
Specifies that db2 can consider the materialized query table in automatic query rewrite. To enable the optimizer to choose the mqt automatically, even when it is not explicitly referenced in the query, as we did in the example above, the enable query optimization must be in effect. If a constraint is not trusted and enabled for query optimization, then it will not. Although though our business is interested only in sumamount, we still have to include count and countamount in the fullselect. Pdf recommending materialized views and indexes with ibm. To enable the optimizer to choose the mqt automatically, the enable query optimization must be in effect it is the default. One of the concerns when customers migrate their system to a new version of db2 is the performance of some of their thousands of sql queries may regress. Db2 10 performance creating a materialized query table. If all of the records for a given date are being deleted from the base table, as in the statement. Query optimization ways of db2 to improve database performance. As it was suggested in ibm manuals that the first time when we populate the data, we should create the mqtwith disable query optimization and then after refresh alter the table to enable query optimization. Mqt optimizes sql performance against data warehouses.
How could the optimizer choose to use the mqt db2 database. To save a pdf on your workstation for viewing or printing. Query optimization with materialized query tables ibm knowledge. After the mqt is populated, enable the table for query optimization. Materialized query tables mqts are a powerful way to improve response time for complex.
Created the mqt with enable query optimization and maintained by user characteristics. After that i refreshed the mqt and populated the data. International technical support organization sql performance diagnosis on ibm db2 universal database for iseries may 2006 sg24665400. Disableenable individual rules generating strategies e. A materialized query table mqt is a table derived from a query result set.
Sas olap server and sas olap cube studio use mqts and db2 cube views19. This happens if another query result set content is completely or partially similar to the mqt. Angelas question is valid and warrants an answer not a workaround. Materialized query tables mqts are a powerful way to improve response time for complex queries.
One of the points of using mqts is that the optimizer is supposed to do query rewrite to use this table. If you dont want the db2 optimizer to utilize an mqt, simply specify the disable query optimization option with the create table statement used to construct the mqt. Terry purcell, ibm lead architect db2 query optimizer may 12, 2016 query optimization and performance with db2. If you enable query optimization for a mqt then the sql is dynamically modified in the database. Ibm 2007 db2 udb query optimizer query graph model qgm captures the entire semantics of the query to be compiled headquarters for all knowledge about compiling. Ibm db2 for i provides two query engines to process queries. Db2 has a feature know as materialized query table mqt which is based. Ive created a usermaintained mqt materialized query table in db2 9. Query optimization ways of db2 to improve the database performance 2. Although an mqt can contain almost any query, the optimizer only supports a. Progressive query optimization for federated queries in db2. If you dont want the db2 optimizer to utilize an mqt, simply specify the disable query optimization option with the create table. Find a technical tutorial in ibm developer find a best practice for integrating.
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