poorbarcode commented on code in PR #20179:
URL: https://github.com/apache/pulsar/pull/20179#discussion_r1199308166
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pulsar-broker/src/main/java/org/apache/pulsar/broker/service/persistent/PersistentStickyKeyDispatcherMultipleConsumers.java:
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@@ -65,23 +67,22 @@ public class PersistentStickyKeyDispatcherMultipleConsumers
extends PersistentDi
private final KeySharedMode keySharedMode;
/**
- * When a consumer joins, it will be added to this map with the current
read position.
- * This means that, in order to preserve ordering, new consumers can only
receive old
- * messages, until the mark-delete position will move past this point.
+ * When a consumer joins, it will be added to this map with the current
last sent position per the message key.
+ * This means that, in order to preserve ordering per the message key, new
consumers can only receive old
+ * messages, until the mark-delete position will move past this point in
the key. New consumers can receive
+ * any new messages with the message key that is not in the last sent
position.
*/
- private final LinkedHashMap<Consumer, PositionImpl>
recentlyJoinedConsumers;
-
- private final Set<Consumer> stuckConsumers;
- private final Set<Consumer> nextStuckConsumers;
+ private final LinkedHashMap<Consumer, LastSentPositions>
recentlyJoinedConsumers;
+ // The lastSentPosition is not thread-safe
+ private final LastSentPositions lastSentPositions;
PersistentStickyKeyDispatcherMultipleConsumers(PersistentTopic topic,
ManagedCursor cursor,
Review Comment:
@equanz
> Could you explain this position in more detail, please? When and how to
get (or calculate?) the position?
It will be set in method `getRestrictedMaxEntriesForConsumer`, let me show a
simpler code
```java
/**
* Calculate how many entries the consumer would consume.
* @param theFirstEntryInCurrentReading This is not the first message the
consumer will receive, but the first message read in this batch.
*/
private synchronized int getRestrictedMaxEntriesForConsumer(Consumer
consumer, List<Entry> entries, ReadType readType, PositionImpl
theFirstEntryInCurrentReading){
if (readType.equals(Normal) ){
recentlyJoinedConsumers.get(consumer).getRight() == null;
recentlyJoinedConsumers.get(consumer).getRight() =
theFirstEntryInCurrentReading;
}
PositionImpl maxReadPosition = getMaxReadPosition(consumer);
...
}
```
The progress runs like this:
| time | `process: add consumer` | `process: in-flight reading` |
| --- | --- | --- |
| 1 | read position is `1:6` |
| 2 | | an in-flight reading which tries to read `1:6~1:10` |
| 3 | Add the new consumer into recently joined consumers |
| 4 | Add new consumer into the selector |
| 5 | | Read entries `1:6 ~ 1:10` complete |
| 6 | | Set read position `1:11` |
| 7 | Set `recentlyJoinedConsumers.consumer.first-position` to `1:11` |
| 8 | | Try to send messages to consumers |
| 9 | | Set `recentlyJoinedConsumers.consumer.second-position` to `1:6`|
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