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Tunning sql query
- 1. Analyze and tuneSQL Query
- 2. Why need tuneSql query Increase performance Save time and money
- 3. Measurement Methods Benchmarking MySQL Enterprise Monitor (MEM), Query Analyzer Performance schema, MySQL sys schema EXPLAIN Optimizer trace Slow log Status variables (SHOW STATUS LIKE ’Handler%’) Profile
- 4. Index Some typeof Index: B-Tree index Hash index R-Tree index The use of indexes to find rows faster Writes become slower with each added index
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- 6. EXPLAIN With EXPLAINthe query is sent all the way to the optimizer, but not to the storage engine Instead EXPLAIN returns the query execution plan EXPLAIN tells you: – In which order the tables are read – What types of read operations that are made – Which indexes could have been used – Which indexes are used – How the tables refer to each other – How many rows the optimizer estimates to retrieve from each table
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- 8. Normalization Normalization isa key factor in optimizing your database structure Good normalization prevents redundant data from being stored in the same tables By moving redundant data to their own table, this reduces storage requirements and overhead when processing queries data warehousing and reporting system a star-schema might be a better solution
- 9. Table Optimizations Usecolumns that are as short as possible; – INT instead of BIGINT – VARCHAR(10) instead of VARCHAR(255) Pay special attention to columns that are used in joins Define columns as NOT NULL if possible
- 10. Index Optimizations Anindex on the whole column is not necessary – Instead index just a prefix of a column – Prefix indexes take less space and the operations are faster Composite indexes can be used for searches on the first column(s) in the index Minimize the size of PRIMARY KEYs that are used as references in other tables Using an auto_increment column can be more optimal A FULLTEXT index is useful for:word searches in text, searches on several columns Click to add text Click to add text
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- 12. Selecting Access Method find the best access method: – Check if the access method is useful – Estimate cost of using access method – Select the cheapest to be used Choice of access method is cost based Finding the optimal method to read data from storage engine Main access methods: - Table scan - Index scan - Ref access - Range scan - Index merge - Loose index scan
- 13. Ref Access id select type tabletype possible key key length ref 1 SIMPLE order ref i_o_orderdate i_o_custkey i_o_orderdat e 4 2 SIMPLE customer eq_ref PRIMARY PRIMARY order.c_cu stkey EXPLAIN SELECT * FROM orders JOIN customer ON c_custkey = o_custkey WHERE o_orderdate = ‘1992-09-12’
- 14. Change Where Condition ToUse Index SELECT * FROM customer WHERE SUBSTRING(c_name,1,1) = 'C' SELECT * FROM customer WHERE c_name >= 'C' and c_name < ‘D’ SELECT * FROM customer WHERE c_name like 'C%'
- 15. Change Where Condition ToUse Index Change where condition into F(field) > const -> filed > G(const)
- 16. Force Index -Ignore Index Select id From data where type = 100 and level > 3 order by id; Select id From data use index(type) where type = 100 and level > 3 order by id; Select id From data ignore index(type) where type = 100 and level > 3 order by id;
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- 19. STRAIGHT_JOIN STRAIGHT_JOIN issimilar to JOIN, except that the left table is always read before the right table. This can be used for those (few) cases for which the join optimizer puts the tables in the wrong order.
- 20. Using Filesort “Filesort”: –Store query result in temporary table before sorting – If data volume is large Optimizations: – index to generate query result in sorted order – For ”LIMIT n” queries.
- 21. Compare Join VsIn SELECT requestID, request_title FROM Request r WHERE EXISTS ( SELECT * FROM User WHERE userID=r.userID ) SELECT requestID, request_title FROM Request r JOIN FROM User USING(serID)
- 22. Join With FederateTable CREATE TABLE federated_table ( id INT(20) NOT NULL AUTO_INCREMENT, name VARCHAR(32) NOT NULL DEFAULT '', other INT(20) NOT NULL DEFAULT '0', PRIMARY KEY (id), INDEX name (name), INDEX other_key (other) ) ENGINE=FEDERATED DEFAULT CHARSET=latin1 CONNECTION='mysql://fed_user@remote_host:9306/federated/test_table' ;
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