[GitHub] [pinot] egalpin commented on a diff in pull request #10880: Fixes #10875 - build forward index if isSorted only results from autogenerated nodict column

["egalpin (via GitHub)" <gi...@apache.org>]

egalpin commented on code in PR #10880:
URL: https://github.com/apache/pinot/pull/10880#discussion_r1224708964


##########
pinot-segment-local/src/main/java/org/apache/pinot/segment/local/segment/index/loader/ForwardIndexHandler.java:
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@@ -359,7 +359,8 @@ private boolean shouldDisableDictionary(String column, ColumnMetadata existingCo
     }
 
     // Sorted columns should always have a dictionary.
-    if (existingColumnMetadata.isSorted()) {
+    if (existingColumnMetadata.isSorted()
+        && !(existingColumnMetadata.getCardinality() == 1 && existingColumnMetadata.isAutoGenerated())) {

Review Comment:
   columns which are auto-generated as part of segment reload after adding a new column always have `cardinality: 1` because the default null value for the column is the sole value in the segment.
   
   When columns have cardinality of 1, they are inferred to be sorted.  It's possible a better fix exists where the noDictColumns can be referenced at the time that "isSorted" is determined. 



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