Tuning Derby Version 10.14 Derby Document build: April 6, 2018, 6:14:42 PM (PDT) Version 10.14 Tuning Derby Contents Copyright................................................................................................................................4 License................................................................................................................................... 5 About this guide....................................................................................................................9 Purpose of this guide................................................................................................9 Audience..................................................................................................................... 9 How this guide is organized.....................................................................................9 Performance tips and tricks.............................................................................................. 10 Use prepared statements with substitution parameters......................................10 Create indexes, and make sure they are being used...........................................10 Ensure that table statistics are accurate.............................................................. 10 Increase the size of the data page cache............................................................. 11 Tune the size of database pages...........................................................................11 Performance trade-offs of large pages............................................................... 12 Avoid expensive queries.........................................................................................13 Use the appropriate getXXX and setXXX methods for the type.......................... 13 Tune database booting/class loading....................................................................14 Avoid inserts in autocommit mode if possible.....................................................14 Improve the performance of table functions........................................................ 14 Configure Derby to use an in-memory database................................................. 15 Increase the concurrency of sequences............................................................... 15 Shut down the system properly.............................................................................15 Put Derby first in your classpath...........................................................................15 Tuning databases and applications..................................................................................17 Application and database design issues.............................................................. 17 Avoiding table scans of large tables................................................................... 17 Avoiding compiling SQL statements................................................................... 19 Shielding users from Derby class-loading events............................................... 21 Analyzing statement execution.............................................................................. 22 Working with RunTimeStatistics............................................................................22 Overview of RunTimeStatistics........................................................................... 22 How you use the RUNTIMESTATISTICS attribute............................................. 23 How you use the XPLAIN style...........................................................................23 Analyzing the information.................................................................................... 25 DML statements and performance....................................................................................31 Performance and optimization............................................................................... 31 Index use and access paths............................................................................... 31 Joins and performance........................................................................................36 Derby's cost-based optimization..........................................................................38 Locking and performance.......................................................................................43 Transaction-based lock escalation...................................................................... 43 Locking a table for the duration of a transaction.................................................44 Non-cost-based optimizations................................................................................44 Non-cost-based sort avoidance (tuple filtering)...................................................44 The MIN() and MAX() optimizations....................................................................46 Overriding the default optimizer behavior............................................................ 46 Selectivity and cardinality statistics................................................................................. 49 Determinations of rows scanned from disk for a table scan.............................. 49 How the optimizer determines the number of rows in a table............................. 49 Estimations of rows scanned from disk for an index scan.................................49 i Version 10.14 Tuning Derby Queries with a known search condition.............................................................. 49 Queries with an unknown search condition........................................................ 50 Statistics-based versus hard-wired selectivity.....................................................50 Selectivity from cardinality statistics....................................................................50 Selectivity from hard-wired assumptions.............................................................51 What are cardinality statistics?..............................................................................51 Working with cardinality statistics.........................................................................52 When cardinality statistics are automatically updated.........................................52 When cardinality statistics go stale..................................................................... 53 Internal language transformations....................................................................................54 Predicate transformations.......................................................................................54 BETWEEN transformations................................................................................. 55 LIKE transformations........................................................................................... 55 Simple IN predicate transformations................................................................... 56 NOT IN predicate transformations...................................................................... 58 OR transformations............................................................................................. 59 Transitive closure.................................................................................................... 59 Transitive closure on join clauses.......................................................................59 Transitive closure on search clauses..................................................................60 View transformations...............................................................................................61 View flattening..................................................................................................... 61 Predicates pushed into views or derived tables..................................................61 Subquery processing and transformations.......................................................... 62 Materialization......................................................................................................62 Flattening a subquery into a normal join.............................................................63 Flattening a subquery into an EXISTS join.........................................................65 Flattening VALUES subqueries...........................................................................66 DISTINCT elimination in IN, ANY, and EXISTS subqueries............................... 66 IN/ANY subquery transformation.........................................................................66 Outer join transformations..................................................................................... 67 Sort avoidance......................................................................................................... 67 DISTINCT elimination based on a uniqueness condition....................................67 Combining ORDER BY and DISTINCT.............................................................. 68 Combining ORDER BY and UNION................................................................... 69 Aggregate processing............................................................................................. 69 COUNT(nonNullableColumn).............................................................................. 69 Trademarks.......................................................................................................................... 70 ii Tuning Derby Apache Software FoundationTuning DerbyApache Derby 3 Tuning Derby Copyright Copyright 2004-2018 The Apache Software