alanlau28 commented on code in PR #23298:
URL: https://github.com/apache/kafka/pull/23298#discussion_r3972814271
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streams/src/main/java/org/apache/kafka/streams/processor/internals/ProcessorStateManager.java:
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@@ -92,13 +92,15 @@ public static class StateStoreMetadata {
// applied to the store used for both restoration (active and standby
tasks restored offset) and
// normal processing that update stores (written offset); could be
null (when initialized)
//
- // the offset is updated in three ways:
+ // the offset is updated in four ways:
// 1. when loading from the checkpoint file, when the corresponding
task has acquired the state
// directory lock and have registered all the state store; it is
only one-time
// 2. when updating with restore records (by both restoring active
and standby),
// update to the last restore record's offset
// 3. when checkpointing with the given written offsets from record
collector,
// update blindly with the given offset
+ // 4. when restoration reaches a confirmed catch-up boundary with no
further records to apply
+ // (KAFKA-14302), as last-applied = next-fetch - 1, never moving
backwards
Review Comment:
Maybe note that standbys reach the *limit* offset, not the end offset?
```java
// 4. when restoration reaches the end offset (the limit offset for
standbys) with no further
// records to apply, update to next-fetch minus one (last-applied);
never moves backwards
```
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