Stamatis Zampetakis created CALCITE-7111:
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Summary: Add an API for finding common relational sub-expressions
Key: CALCITE-7111
URL: https://issues.apache.org/jira/browse/CALCITE-7111
Project: Calcite
Issue Type: Improvement
Components: core
Reporter: Stamatis Zampetakis
Assignee: Stamatis Zampetakis
There have been various tickets (CALCITE-5631) and
[discussions|https://lists.apache.org/thread/oj7kzz39n4jn0jj7vgflzwl5xr65s3h5]
touching the problem of optimizing queries with common sub-expressions. A
recurrent need is given a query/plan/RelNode to identify common sub-expressions
and for that purpose multiple algorithms can be developed with different
trade-offs. Someone may opt to implement a complex algorithm from a research
paper based on integer linear programming (ILP) while another one may simply go
for a structure based traversal.
The goal of this ticket is to introduce a simple interface that given a RelNode
finds/detects/suggests common sub-expressions.
{code:java}
@API(since = "1.41.0", status = API.Status.EXPERIMENTAL)
public interface RelCommonExpressionSuggester {
Collection<RelNode> suggest(RelNode input, Context context);
}
{code}
The interface and its Javadoc will go along with a simple implementation
detecting exact matches and some tests.
The main motivation behind this proposal comes from Apache Hive and Apache
Impala that aim to exploit common sub-expressions during planning. Instead of
crafting separate interfaces for each project or copy-pasting code around it is
natural to have the basic interfaces in calcite-core. Moreover, this proposal
allows closed source implementations of the interface to be used in each
project without ending up with contrived cyclic dependencies.
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