[GitHub] [incubator-pinot] Jackie-Jiang commented on a change in pull request #4051: Fix the race condition for real-time inverted index reader

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Jackie-Jiang commented on a change in pull request #4051: Fix the race condition for real-time inverted index reader
URL: https://github.com/apache/incubator-pinot/pull/4051#discussion_r271425667
 
 

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 File path: pinot-core/src/main/java/org/apache/pinot/core/realtime/impl/invertedindex/RealtimeInvertedIndexReader.java
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 @@ -60,6 +60,13 @@ public MutableRoaringBitmap getDocIds(int dictId) {
     ThreadSafeMutableRoaringBitmap bitmap;
     try {
       _readLock.lock();
+      // NOTE: the given dict Id might not be added to the inverted index yet. We first add the value to the dictionary.
+      // Before the value is added to the inverted index, the query might have a predicate which matches the newly added
+      // value. In that case, the given dictionary Id does not exist in the inverted index, and we return an empty
+      // bitmap.
+      if (_bitmaps.size() == dictId) {
 
 Review comment:
   @kishoreg Actually you are right for multi-valued column. I'll change this to `_bitmaps.size() <= dictId` to handle all cases.
   In the ancient code, we might return null, but then we refactored the code and uniformed the interface. Right now the interface does not expect null return value, and this is corner case which happens rarely, so I would rather handle this inside the implementation by returning an empty bitmap instead of null.

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