Rui Fan created FLINK-40359:
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Summary: Split FetchedChannelStateReader into drain-side and
checkpoint-side interfaces
Key: FLINK-40359
URL: https://issues.apache.org/jira/browse/FLINK-40359
Project: Flink
Issue Type: Technical Debt
Components: Runtime / Checkpointing
Affects Versions: 2.4.0
Reporter: Rui Fan
Assignee: Rui Fan
FetchedChannelStateReader currently serves two call sites: the drain path, which
reads segments into the input channels, commits what it delivered and derives
snapshots; and the checkpoint path, which only replays the segments of a
snapshot
into the checkpoint stream. commit() and snapshot() are meaningless on the
checkpoint path, but nothing prevents calling them — the rule only exists in
javadoc.
Proposal: a read-only interface for the checkpoint path, and a drain-side
interface extending it with commit() and snapshot(), so the constraint is
enforced
by the compiler. The implementation can stay shared (inheritance or
encapsulation).
One thing to settle while implementing: commit() sits on SpillSegment, so hiding
it from the checkpoint path requires either a generic reader, a second segment
type, or moving commit() up onto the drain-side reader.
Refactoring only, no functional change.
More details can be found from
https://github.com/apache/flink/pull/28661#discussion_r3693955957
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