klsince commented on code in PR #13285:
URL: https://github.com/apache/pinot/pull/13285#discussion_r1634137440


##########
pinot-core/src/main/java/org/apache/pinot/core/data/manager/realtime/RealtimeSegmentDataManager.java:
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@@ -703,9 +703,20 @@ public void run() {
         //   persisted.
         // Take upsert snapshot before starting consuming events
         if (_partitionUpsertMetadataManager != null) {
-          _partitionUpsertMetadataManager.takeSnapshot();
-          // If upsertTTL is enabled, we will remove expired primary keys from 
upsertMetadata after taking snapshot.
-          _partitionUpsertMetadataManager.removeExpiredPrimaryKeys();
+          if (_tableConfig.getUpsertMetadataTTL() > 0) {
+            // If upsertMetadataTTL is enabled, we will remove expired primary 
keys from upsertMetadata
+            // AFTER taking a snapshot. Taking the snapshot first is crucial 
to ensure we capture the final
+            // state of a particular key before it exits the TTL window.

Review Comment:
   I see, that makes sense. Based on the metadata TTL related code, it seems 
like taking snapshot after removing metadata out of the TTL wouldn’t affect 
data/query correctness but incurred some extra overhead if server restarted 
before taking new snapshot as it had to add metadata (already out of TTL) back 
to Map, however those metadata would be removed again. 
   
   IIUC, maybe update the comment a bit that this is mainly to avoid such 
overhead upon unexpected server restart, but not affecting correctness. 
   



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