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SQL Tuning Scripts

SQL Tuning Scripts. Bobby Durrett US Foodservice bobbyandmarielle@yahoo.com http://www.geocities.com/bobbyandmarielle/seouc.zip. Tuning a slow SQL statement. Create directory with tuning scripts Capture problem SQL Get execution plan Query DBA_ views Run select count(*) queries

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SQL Tuning Scripts

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  1. SQL Tuning Scripts Bobby Durrett US Foodservice bobbyandmarielle@yahoo.com http://www.geocities.com/bobbyandmarielle/seouc.zip

  2. Tuning a slow SQL statement • Create directory with tuning scripts • Capture problem SQL • Get execution plan • Query DBA_ views • Run select count(*) queries • Try different plans • Test execution of improved SQL

  3. Why these scripts? • DBA view columns used by optimizer • Tables in problem SQL only • Records current state of statistics • Readable format • Only needs SQL*Plus • Free!

  4. Script names • tablelist.sql – tables in query • tablestats.sql – table level statistics • indexstats.sql – index level statistics • indexcolumns.sql – columns in indexes • columnstats.sql – column level stats • histograms.sql – histogram details • all.sql – runs all of the above

  5. Example • Table TEST – 2,000,001 rows • Columns A, B – NUMBER • 1,000,000 rows (1,1) • 1,000,000 rows (2,2) • 1 row (1,2) • Query where condition A=1, B=2 chooses the one row

  6. tablelist.sql • Edit to include owner, table_name for each table in problem SQL • May have to expand views to get base tables • Can also get table names from plan

  7. tablestats.sql • OWNER • TABLE_NAME • NUM_ROWS • BLOCKS • AVG_ROW_LEN • SAMPLE_SIZE • LAST_ANALYZED

  8. indexstats.sql • TABLE_OWNER • TABLE_NAME • INDEX_NAME • NUM_ROWS • SAMPLE_SIZE • CLUSTERING_FACTOR • LAST_ANALYZED • LEAF_BLOCKS • DISTINCT_KEYS • AVG_LEAF_BLOCKS_PER_KEY • AVG_DATA_BLOCKS_PER_KEY • BLEVEL

  9. indexcolumns.sql • TABLE_NAME • INDEX_NAME • COLUMN_NAME • COLUMN_EXPRESSION

  10. columnstats.sql • TABLE_NAME • COLUMN_NAME • LO • HI • NUM_DISTINCT • NUM_BUCKETS • DENSITY • NUM_NULLS • AVG_COL_LEN • LAST_ANALYZED • SAMPLE_SIZE

  11. histograms.sql • HISTOGRAM • TABLE_NAME • COLUMN_NAME • ENDPOINT_NUMBER • ENDPOINT_VALUE • ENDPOINT_ACTUAL_VALUE

  12. References • http://www.geocities.com/bobbyandmarielle/sqltuning.zip - My talk on cardinality issues • Cost Based Optimizer Fundamentals, Jonathan Lewis • Metalink Note:212809.1, Limitations of the Oracle Cost Based Optimizer • Metalink Note:68992.1, Predicate Selectivity • Histograms – Myths and Facts, Wolfgang Breitling, Select Journal, Volume 13, Number 3

  13. SQL Tuning Scripts Bobby Durrett US Foodservice bobbyandmarielle@yahoo.com http://www.geocities.com/bobbyandmarielle/seouc.zip

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