Robert Burke created BEAM-11097:
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Summary: [Go SDK] Windowed Side Input Caching
Key: BEAM-11097
URL: https://issues.apache.org/jira/browse/BEAM-11097
Project: Beam
Issue Type: Improvement
Components: sdk-go
Reporter: Robert Burke
Side inputs are valid for given window. That means they can be and correctly
cached and re-used in multiple bundles if the data has already been loaded into
a given worker.
Care needs to be taken to allow the data to be garbage collected if it hasn't
been used in the last minute or so. In practice, Global Window side inputs will
not be evicted while still in use, but infrequently accessed data will possibly
be evicted more regularly. A limit should be set to avoid running out of memory.
As presently implemented, each ProcessElement call (or StartBundle or
FinishBundle) will only query for side input data on user request. However,
results of user requests are not cached between elements or bundles, which
means there's additional lookup and serialization time from the runner side.
It may be possible to re-use allocated side input elements, but even a solution
that re-decodes data on every call would be an improvement if the data isn't
re-streamed from the runner.
If https://issues.apache.org/jira/browse/BEAM-3293 has been implemented, then
per-key+window caching should additionally be considered for more granular
caching of data.
This optimization has an outsized impact on streaming performance as side input
data can change per bundle, and streaming bundles are typically small, and
quickly processed.
This work would be implemented in the exec package:
https://github.com/apache/beam/blob/master/sdks/go/pkg/beam/core/runtime/exec/sideinput.go
and probably the harness package
https://github.com/apache/beam/blob/c185adb7652034b5d044aae65a1a972d9ceb4377/sdks/go/pkg/beam/core/runtime/harness/statemgr.go#L50
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