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[SPARK-20881] [SQL] Clearly document the mechanism to choose between two sources of statistics #18105

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[SPARK-20881] [SQL] Clearly document the mechanism to choose between two sources of statistics #18105

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4 changes: 3 additions & 1 deletion sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveExternalCatalog.scala
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Expand Up @@ -681,9 +681,11 @@ private[spark] class HiveExternalCatalog(conf: SparkConf, hadoopConf: Configurat
}
}

// construct Spark's statistics from information in Hive metastore
// Restore Spark's statistics from information in Metastore.
val statsProps = table.properties.filterKeys(_.startsWith(STATISTICS_PREFIX))

// Currently we have two sources of statistics: one from Hive and the other from Spark.
// In our design, if Spark's statistics is available, we respect it over Hive's statistics.
if (statsProps.nonEmpty) {
val colStats = new mutable.HashMap[String, ColumnStat]

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2 changes: 2 additions & 0 deletions sql/hive/src/main/scala/org/apache/spark/sql/hive/client/HiveClientImpl.scala
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Expand Up @@ -434,6 +434,8 @@ private[hive] class HiveClientImpl(
}
val comment = properties.get("comment")

// Here we are reading statistics from Hive.
// Note that this statistics could be overridden by Spark's statistics if that's available.
val totalSize = properties.get(StatsSetupConst.TOTAL_SIZE).map(BigInt(_))
val rawDataSize = properties.get(StatsSetupConst.RAW_DATA_SIZE).map(BigInt(_))
val rowCount = properties.get(StatsSetupConst.ROW_COUNT).map(BigInt(_)).filter(_ >= 0)
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