[GitHub] [spark] kiszk commented on a change in pull request #29654: [SPARK-32802][SQL] Avoid using SpecificInternalRow in RunLengthEncoding#Encoder

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kiszk commented on a change in pull request #29654:
URL: https://github.com/apache/spark/pull/29654#discussion_r486972465



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File path: sql/core/src/main/scala/org/apache/spark/sql/execution/columnar/compression/compressionSchemes.scala
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@@ -195,16 +193,16 @@ private[columnar] case object RunLengthEncoding extends CompressionScheme {
       val actualSize = columnType.actualSize(row, ordinal)
       _uncompressedSize += actualSize
 
-      if (lastValue.isNullAt(0)) {
-        columnType.copyField(row, ordinal, lastValue, 0)
+      if (lastValue == null) {
+        lastValue = columnType.clone(columnType.getField(row, ordinal))

Review comment:
       Do we need `clone()` here?  While I guess that this is for `UTF8String`, `lastValue` is used only for keeping a value. Thus, it is ok with just keeping the reference for `UTF8String`.




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