Luke Cwik created BEAM-13930:
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Summary: Address StateSpec inconsistency between Runner and Fn API
Key: BEAM-13930
URL: https://issues.apache.org/jira/browse/BEAM-13930
Project: Beam
Issue Type: Improvement
Components: beam-model, sdk-java-core, sdk-py-core
Reporter: Luke Cwik
Assignee: Luke Cwik
The ability to mix and match runners and SDKs is accomplished through two
portability layers:
1. The Runner API provides an SDK-and-runner-independent definition of a Beam
pipeline
2. The Fn API allows a runner to invoke SDK-specific user-defined functions
Apache Beam pipelines support executing stateful DoFns[1]. To support this
execution the Runner API defines multiple user state specifications:
* ReadModifyWriteStateSpec
* BagStateSpec
* OrderedListStateSpec
* CombiningStateSpec
* MapStateSpec
* SetStateSpec
The Fn API[2] defines APIs[3] to get, append and clear user state currently
supporting a BagUserState and MultimapUserState protocol.
Since there is no clear mapping between the Runner API and Fn API state
specifications, there is no way for a runner to know that it supports a given
API necessary to support the execution of the pipeline. The Runner will also
have to manage additional runtime metadata associated with which protocol was
used for a type of state so that it can successfully manage the state’s
lifetime once it can be garbage collected.
Please see the doc[4] for further details and a proposal on how to address this
shortcoming.
1: https://beam.apache.org/blog/stateful-processing/
2:
https://github.com/apache/beam/blob/3ad05523f4cdf5122fc319276fcb461f768af39d/model/fn-execution/src/main/proto/beam_fn_api.proto#L742
3: https://s.apache.org/beam-fn-state-api-and-bundle-processing
4: http://doc/1ELKTuRTV3C5jt_YoBBwPdsPa5eoXCCOSKQ3GPzZrK7Q
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