[GitHub] [druid] jasonk000 commented on a change in pull request #12105: perf: indexing: Introduce a bulk getValuesInto function to read values

[GitBox <gi...@apache.org>]

jasonk000 commented on a change in pull request #12105:
URL: https://github.com/apache/druid/pull/12105#discussion_r776540734



##########
File path: processing/src/main/java/org/apache/druid/segment/DimensionDictionary.java
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@@ -84,6 +84,19 @@ public T getValue(int id)
     }
   }
 
+  public void getValuesInto(int[] ids, T[] values)
+  {
+    lock.readLock().lock();
+    try {
+      for (int i = 0; i < ids.length; i++) {

Review comment:
       Good point on checking array lengths match.
   
   I did explore returning value only (that's my internal impl actually), but it requires wider changes. Specifically, since Java erases generics, it's impossible to do `new T[]`. So, we have to either do something like:
   ```
   StringDimensionIndexer() constructor {
   super(String.class);
   }
   
   // and then propagate this Class<T> to DimensionDictionary, and in DimensionDictionary, do a:
   
   T[] out = (T[]) Array.newInstance(typeFromConstructor, keys.length);
   ```
   To me, both are viable and work fine, this approach seems less invasive.
   
   What do you suggest?




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