felixcheung commented on a change in pull request #25789: [SPARK-28927][ML]
Show warning when input data to ALS is indeterminate
URL: https://github.com/apache/spark/pull/25789#discussion_r324443661
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File path: mllib/src/main/scala/org/apache/spark/ml/recommendation/ALS.scala
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@@ -920,6 +924,14 @@ object ALS extends DefaultParamsReadable[ALS] with
Logging {
require(intermediateRDDStorageLevel != StorageLevel.NONE,
"ALS is not designed to run without persisting intermediate RDDs.")
+ // Indeterminate rating RDD causes inconsistent in/out blocks in case of
rerun.
+ // It can cause runtime error when matching in/out user/item blocks.
+ if (ratings.outputDeterministicLevel == DeterministicLevel.INDETERMINATE) {
Review comment:
if I understanding this correctly, mismatch -> failure is only one possible
outcome? it could also end up matching the wrong user/item before the index is
wrong? that seems more subtle and much harder to detect
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