Yifan Mai created BEAM-10409:
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Summary: Combiner Packing Graph Optimization
Key: BEAM-10409
URL: https://issues.apache.org/jira/browse/BEAM-10409
Project: Beam
Issue Type: Improvement
Components: runner-core
Reporter: Yifan Mai
Assignee: Yifan Mai
Some use cases of Beam (e.g. [TensorFlow
Transform|https://github.com/tensorflow/transform]) create thousands of Combine
stages with a common parent. The large number of stages can cause performance
issues on some runners. To alleviate, a graph optimization phase could be added
to the translations module that packs compatible Combine stages into a single
stage.
The graph optimization for CombinePerKey would work as follows: If
CombinePerKey stages have a common input, one input each, and one output each,
pack the stages into a single stage that runs all CombinePerKeys and outputs
resulting tuples to a new PCollection. A subsequent stage unpacks tuples from
this PCollection and sends them to the original output PCollections.
There is an additional issue with supporting this for CombineGlobally: because
of the intermediate KeyWithVoid stage between the CombinePerKey stages and the
input stage, the CombinePerKey stages do not have a common input stage, and
cannot be packed. To support CombineGlobally, a common sibling elimination
graph optimization phase can be used to combine the KeyWithVoid stages. After
this, the CombinePerKey stages would have a common input and can be packed.
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