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A recent change, IMPALA-5016, added an expr rewrite rule to simplfy coalesce(). This rule eliminates the coalesce() when its first parameter (that isn't constant null) is a SlotRef pointing to a SlotDescriptor that is non-nullable (for example because it is from a non-nullable Kudu column or because it is from an HDFS partition column with no null partitions), under the assumption that the SlotRef could never have a null value. This assumption is violated when the SlotRef is the output of an outer join, leading to incorrect results being returned. The problem is that the nullability of a SlotDescriptor (which determines whether there is a null indicator bit in the tuple for that slot) is a slightly different property than the nullability of a SlotRef pointing to that SlotDescriptor (since the SlotRef can still be NULL if the entire tuple is NULL). This patch removes the portion of the rewrite rule that considers the nullability of the SlotDescriptor. This means that we're missing out on some optimizations opportunities and we should revisit this in a way that works with outer joins (IMPALA-5753) Testing: - Updated FE tests. - Added regression tests to exprs.test Change-Id: I1ca6df949f9d416ab207016236dbcb5886295337 Reviewed-on: http://gerrit.cloudera.org:8080/7567 Reviewed-by: Matthew Jacobs <mj@cloudera.com> Reviewed-by: Thomas Tauber-Marshall <tmarshall@cloudera.com> Tested-by: Impala Public Jenkins
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 and Amazon S3.
- Wide analytic SQL support, including window functions and subqueries.
- On-the-fly code generation using LLVM to generate CPU-efficient code tailored specifically to each individual query.
- Support for the most commonly-used Hadoop file formats, including the Apache Parquet (incubating) project.
- 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.
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.
Build Instructions
See bin/bootstrap_build.sh.
Export Control Notice
This distribution uses cryptographic software and may be subject to export controls. Please refer to EXPORT_CONTROL.md for more information.