[SPARK-56798][SQL][DOCS] Clarify streaming CDC emission timing and netChanges scope#55776
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gengliangwang wants to merge 1 commit intoapache:masterfrom
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[SPARK-56798][SQL][DOCS] Clarify streaming CDC emission timing and netChanges scope#55776gengliangwang wants to merge 1 commit intoapache:masterfrom
gengliangwang wants to merge 1 commit intoapache:masterfrom
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…tChanges scope Address two follow-up review threads on PR apache#55637 (streaming CDC netChanges): - The "held back" paragraph was worded as if the one-commit emission lag were a netChanges-specific property. It is not -- carry-over removal and update detection use append-mode `Aggregate` keyed on `_commit_timestamp` and have the same lag as the netChanges `transformWithState` timer. - Set realistic expectations for streaming netChanges: for typical CDC sources that produce at most one change per row per commit, the streaming output equals what `computeUpdates` would produce, because only one commit's changes are buffered at a time. Cross-commit merging only kicks in when several commits touch the same row before the older one's output is emitted. Direct users to a batch read for full-range collapse. Both points are now stated up-front in plain language, with a bulleted list and short bold labels for scannability.
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What changes were proposed in this pull request?
Address two follow-up review threads on PR #55637 (streaming CDC netChanges) by clarifying the streaming behavior in the
ChangelogJavadoc.The previous paragraph read as if the one-commit emission lag were a netChanges-specific property; in fact carry-over removal and update detection use append-mode
Aggregatekeyed on_commit_timestampand have the same lag as the netChangestransformWithStatetimer. The paragraph also did not set expectations for what streaming netChanges actually collapses in practice.Replaced the existing single paragraph with a bulleted list:
computeUpdates. Multiple commits' changes are merged only when those commits touch the same row before the older one's output has been emitted. For full-range collapse, use a batch read.This is a sub-task of SPARK-55668.
Why are the changes needed?
Spelling out the emission timing and the practical netChanges scope prevents adopters from forming wrong expectations about what streaming netChanges does for typical (atomic-commit) CDC workloads. Naming the lag and the buffer-window scope explicitly also makes the doc consistent with the implementation, where both facts are properties of all three streaming post-processing paths.
Does this PR introduce any user-facing change?
Documentation only. No behavior change.
How was this patch tested?
Doc-only change.
Xdoclint:html,syntax,accessibilityis clean onChangelog.java(errors limited to expected "cannot find symbol" without classpath). No code changed; existing CDC test suites unaffected.Was this patch authored or co-authored using generative AI tooling?
Generated-by: Claude opus-4-7