[BEAM-8549] Do not use keyed operator state for checkpoint buffering #9993
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The current buffer logic for items emitted during checkpointing is faulty in the sense that the buffer is partitioned on the output keys of the operator. The key may be changed or even be dropped. Thus, the original key partitioning will not be maintained which will cause checkpointing to fail. An alternative solution would be BEAM-6733 / apache#9652, but this change keeps the current buffering logic in place. The output buffer may now always be redistributed round-robin upon restoring from a checkpoint. Note that this is fine because no assumption can be made about the distribution of output elements of a DoFn operation.
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tweise
approved these changes
Nov 5, 2019
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The current buffer logic for items emitted during checkpointing is faulty in the
sense that the buffer is partitioned on the output keys of the operator. The key
may be changed or even be dropped. Thus, the original key partitioning will not
be maintained which will cause checkpointing to fail.
An alternative solution would be BEAM-6733 / #9652, but this change keeps the
current buffering logic in place. The output buffer may now always be
redistributed round-robin upon restoring from a checkpoint. Note that this is
fine because no assumption can be made about the distribution of output elements
of a DoFn operation.
Backport of #9980.
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