[GitHub] jon-wei commented on a change in pull request #6724: Fix issue that tasks failed because of no sink for identifier

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jon-wei commented on a change in pull request #6724: Fix issue that tasks failed because of no sink for identifier
URL: https://github.com/apache/incubator-druid/pull/6724#discussion_r243482186
 
 

 ##########
 File path: server/src/main/java/org/apache/druid/segment/realtime/appenderator/AppenderatorImpl.java
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 @@ -485,8 +486,12 @@ public void clear() throws InterruptedException
     final List<Pair<FireHydrant, SegmentIdentifier>> indexesToPersist = new ArrayList<>();
     int numPersistedRows = 0;
     long bytesPersisted = 0L;
-    for (SegmentIdentifier identifier : sinks.keySet()) {
-      final Sink sink = sinks.get(identifier);
+    Iterator<Map.Entry<SegmentIdentifier, Sink>> iterator = sinks.entrySet().iterator();
+
+    while (iterator.hasNext()) {
 
 Review comment:
   If I understand correctly, from the code in `abandonSegment`, it looks like the sink removal should not be happening at the same time as a persist (they're both run by the `persistExecutor`).
   
   With this change to using an iterator, I think it would now be possible to persist a Sink that was already abandoned (i.e., `abandonSegment` could remove a Sink after that Sink is returned by iterator.next() in `persistAll`)).
   
   So I'm wondering if it would be more correct to have this "find sinks to persist" code run in one callable together with the actual persist work in the `persistExecutor` as well. 
   
   ----
   
   There is also a code block in `push` that has a similar pattern that runs outside of the `pushExecutor` (`abandonSegment` uses `pushBarrier()`), I wonder if there are similar problems there as well:
   
   ```
   final Map<SegmentIdentifier, Sink> theSinks = new HashMap<>();
       for (final SegmentIdentifier identifier : identifiers) {
         final Sink sink = sinks.get(identifier);
         if (sink == null) {
           throw new ISE("No sink for identifier: %s", identifier);
         }
         theSinks.put(identifier, sink);
         if (sink.finishWriting()) {
           totalRows.addAndGet(-sink.getNumRows());
         }
       }
   ```

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