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When generating plans with left semi/anti joins (typically resulting from subquery rewrites), the planner now considers inserting a distinct aggregation on the inner side of the join. The decision is based on whether that aggregation would reduce the number of rows by more than 75%. This is fairly conservative and the optimization might be beneficial for smaller reductions, but the conservative threshold is chosen to reduce the number of potential plan regressions. The aggregation can both reduce the # of rows and the width of the rows, by projecting out unneeded slots. ENABLE_DISTINCT_SEMI_JOIN_OPTIMIZATION query option is added to allow toggling the optimization. Tests: * Add positive and negative planner tests for various cases - including semi/anti joins, missing stats, broadcast/shuffle, different numbers of join predicates. * Add some end-to-end tests to verify plans execute correctly. Change-Id: Icbb955e805d9e764edf11c57b98f341b88a37fcc Reviewed-on: http://gerrit.cloudera.org:8080/16180 Reviewed-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com> Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
Welcome to Impala
Lightning-fast, distributed SQL queries for petabytes of data stored in Apache Hadoop clusters.
Impala is a modern, massively-distributed, massively-parallel, C++ query engine that lets you analyze, transform and combine data from a variety of data sources:
- Best of breed performance and scalability.
- Support for data stored in HDFS, Apache HBase, Apache Kudu, Amazon S3, Azure Data Lake Storage, Apache Hadoop Ozone and more!
- Wide analytic SQL support, including window functions and subqueries.
- On-the-fly code generation using LLVM to generate lightning-fast code tailored specifically to each individual query.
- Support for the most commonly-used Hadoop file formats, including Apache Parquet and Apache ORC.
- Support for industry-standard security protocols, including Kerberos, LDAP and TLS.
- Apache-licensed, 100% open source.
More about Impala
To learn more about Impala as a business user, or to try Impala live or in a VM, please visit the Impala homepage. Detailed documentation for administrators and users is available at Apache Impala documentation.
If you are interested in contributing to Impala as a developer, or learning more about Impala's internals and architecture, visit the Impala wiki.
Supported Platforms
Impala only supports Linux at the moment.
Export Control Notice
This distribution uses cryptographic software and may be subject to export controls. Please refer to EXPORT_CONTROL.md for more information.
Build Instructions
See Impala's developer documentation to get started.
Detailed build notes has some detailed information on the project layout and build.