[GitHub] [iceberg] szehon-ho commented on a diff in pull request #3457: Spark: Improve performance of expire snapshot by not double-scanning retained Snapshots

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

szehon-ho commented on code in PR #3457:
URL: https://github.com/apache/iceberg/pull/3457#discussion_r933684634


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spark/v3.2/spark/src/main/java/org/apache/iceberg/spark/actions/ExpireSnapshotsSparkAction.java:
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@@ -171,11 +173,15 @@ public Dataset<Row> expire() {
 
       expireSnapshots.commit();
 
-      // fetch metadata after expiration
-      Dataset<Row> validFiles = buildValidFileDF(ops.refresh());
+      TableMetadata updatedTable = ops.refresh();
+      Set<Long> retainedSnapshots =
+          updatedTable.snapshots().stream().map(Snapshot::snapshotId).collect(Collectors.toSet());
+      Dataset<Row> validFiles = buildValidFileDF(updatedTable);
+      Dataset<Row> deleteCandidateFiles =

Review Comment:
   Sure, it makes sense to me, can make the change.
   
   I had the optimization in the end to pass the lesser of the two sets to Spark , with either 'in' or 'not in', but can still do it the other way.



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