chore: disable xxhash64 by default

common/src/main/scala/org/apache/comet/CometConf.scala

@@ -401,6 +401,12 @@ object CometConf extends ShimCometConf {
       .booleanConf
       .createWithDefault(false)
 
+  val COMET_XXHASH64_ENABLED: ConfigEntry[Boolean] =
+    conf("spark.comet.xxhash64.enabled")
+      .doc("The xxhash64 implementation is not optimized yet and may cause performance issues.")
+      .booleanConf
+      .createWithDefault(false)
+
 }
 
 object ConfigHelpers {

docs/source/user-guide/configs.md

@@ -48,3 +48,4 @@ Comet provides the following configuration settings.
 | spark.comet.scan.preFetch.enabled | Whether to enable pre-fetching feature of CometScan. By default is disabled. | false |
 | spark.comet.scan.preFetch.threadNum | The number of threads running pre-fetching for CometScan. Effective if spark.comet.scan.preFetch.enabled is enabled. By default it is 2. Note that more pre-fetching threads means more memory requirement to store pre-fetched row groups. | 2 |
 | spark.comet.shuffle.preferDictionary.ratio | The ratio of total values to distinct values in a string column to decide whether to prefer dictionary encoding when shuffling the column. If the ratio is higher than this config, dictionary encoding will be used on shuffling string column. This config is effective if it is higher than 1.0. By default, this config is 10.0. Note that this config is only used when 'spark.comet.columnar.shuffle.enabled' is true. | 10.0 |
+| spark.comet.xxhash64.enabled | The xxhash64 implementation is not optimized yet and may cause performance issues. | false |

spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala

@@ -2101,19 +2101,27 @@ object QueryPlanSerde extends Logging with ShimQueryPlanSerde with CometExprShim
           scalarExprToProtoWithReturnType("murmur3_hash", IntegerType, exprs :+ seedExpr: _*)
 
         case XxHash64(children, seed) =>
-          val firstUnSupportedInput = children.find(c => !supportedDataType(c.dataType))
-          if (firstUnSupportedInput.isDefined) {
-            withInfo(expr, s"Unsupported datatype ${firstUnSupportedInput.get.dataType}")
-            return None
+          if (CometConf.COMET_XXHASH64_ENABLED.get()) {
+            val firstUnSupportedInput = children.find(c => !supportedDataType(c.dataType))
+            if (firstUnSupportedInput.isDefined) {
+              withInfo(expr, s"Unsupported datatype ${firstUnSupportedInput.get.dataType}")
+              return None
+            }
+            val exprs = children.map(exprToProtoInternal(_, inputs))
+            val seedBuilder = ExprOuterClass.Literal
+              .newBuilder()
+              .setDatatype(serializeDataType(LongType).get)
+              .setLongVal(seed)
+            val seedExpr = Some(ExprOuterClass.Expr.newBuilder().setLiteral(seedBuilder).build())
+            // the seed is put at the end of the arguments
+            scalarExprToProtoWithReturnType("xxhash64", LongType, exprs :+ seedExpr: _*)
+          } else {
+            withInfo(
+              expr,
+              "xxhash64 is disabled by default. " +
+                s"Set ${CometConf.COMET_XXHASH64_ENABLED.key}=true to enable it.")
+            None
           }
-          val exprs = children.map(exprToProtoInternal(_, inputs))
-          val seedBuilder = ExprOuterClass.Literal
-            .newBuilder()
-            .setDatatype(serializeDataType(LongType).get)
-            .setLongVal(seed)
-          val seedExpr = Some(ExprOuterClass.Expr.newBuilder().setLiteral(seedBuilder).build())
-          // the seed is put at the end of the arguments
-          scalarExprToProtoWithReturnType("xxhash64", LongType, exprs :+ seedExpr: _*)
 
         case Sha2(left, numBits) =>
           if (!numBits.foldable) {

spark/src/test/scala/org/apache/comet/CometExpressionSuite.scala

@@ -1489,6 +1489,7 @@ class CometExpressionSuite extends CometTestBase with AdaptiveSparkPlanHelper {
     Seq(true, false).foreach { dictionary =>
       withSQLConf(
         "parquet.enable.dictionary" -> dictionary.toString,
+        CometConf.COMET_XXHASH64_ENABLED.key -> "true",
         CometConf.COMET_CAST_ALLOW_INCOMPATIBLE.key -> "true") {
         val table = "test"
         withTable(table) {
@@ -1521,6 +1522,7 @@ class CometExpressionSuite extends CometTestBase with AdaptiveSparkPlanHelper {
     Seq(true, false).foreach { dictionary =>
       withSQLConf(
         "parquet.enable.dictionary" -> dictionary.toString,
+        CometConf.COMET_XXHASH64_ENABLED.key -> "true",
         CometConf.COMET_CAST_ALLOW_INCOMPATIBLE.key -> "true") {
         val table = "test"
         withTable(table) {