Github user cloud-fan commented on a diff in the pull request:

    https://github.com/apache/spark/pull/15158#discussion_r79656655
  
    --- Diff: 
sql/hive/src/main/scala/org/apache/spark/sql/hive/MetastoreRelation.scala ---
    @@ -109,39 +109,59 @@ private[hive] case class MetastoreRelation(
       }
     
       @transient override lazy val statistics: Statistics = {
    -    catalogTable.stats.getOrElse(Statistics(
    -      sizeInBytes = {
    -        val totalSize = 
hiveQlTable.getParameters.get(StatsSetupConst.TOTAL_SIZE)
    -        val rawDataSize = 
hiveQlTable.getParameters.get(StatsSetupConst.RAW_DATA_SIZE)
    -        // TODO: check if this estimate is valid for tables after 
partition pruning.
    -        // NOTE: getting `totalSize` directly from params is kind of 
hacky, but this should be
    -        // relatively cheap if parameters for the table are populated into 
the metastore.
    -        // Besides `totalSize`, there are also `numFiles`, `numRows`, 
`rawDataSize` keys
    -        // (see StatsSetupConst in Hive) that we can look at in the future.
    -        BigInt(
    -          // When table is external,`totalSize` is always zero, which will 
influence join strategy
    -          // so when `totalSize` is zero, use `rawDataSize` instead
    -          // when `rawDataSize` is also zero, use 
`HiveExternalCatalog.STATISTICS_TOTAL_SIZE`,
    -          // which is generated by analyze command.
    -          if (totalSize != null && totalSize.toLong > 0L) {
    -            totalSize.toLong
    -          } else if (rawDataSize != null && rawDataSize.toLong > 0) {
    -            rawDataSize.toLong
    -          } else if 
(sparkSession.sessionState.conf.fallBackToHdfsForStatsEnabled) {
    -            try {
    -              val hadoopConf = sparkSession.sessionState.newHadoopConf()
    -              val fs: FileSystem = 
hiveQlTable.getPath.getFileSystem(hadoopConf)
    -              fs.getContentSummary(hiveQlTable.getPath).getLength
    -            } catch {
    -              case e: IOException =>
    -                logWarning("Failed to get table size from hdfs.", e)
    -                sparkSession.sessionState.conf.defaultSizeInBytes
    -            }
    -          } else {
    -            sparkSession.sessionState.conf.defaultSizeInBytes
    -          })
    +    catalogTable.stats.getOrElse {
    +      // For non-partitioned tables, Hive-generated statistics are stored 
in table properties
    +      // For partitioned tables, Hive-generated statistics are stored in 
partition properties
    +      val (totalSize, rawDataSize) = if 
(catalogTable.partitionColumnNames.isEmpty) {
    +        val properties = 
Option(hiveQlTable.getParameters).map(_.asScala.toMap).orNull
    +        (properties.get(StatsSetupConst.TOTAL_SIZE).map(_.toLong),
    +          properties.get(StatsSetupConst.RAW_DATA_SIZE).map(_.toLong))
    +      } else {
    +        (getTotalTableSize(StatsSetupConst.TOTAL_SIZE),
    +          getTotalTableSize(StatsSetupConst.RAW_DATA_SIZE))
           }
    -    ))
    +      Statistics(
    +        sizeInBytes = {
    +          BigInt(
    +            // When table is external,`totalSize` is always zero, which 
will influence join strategy
    +            // so when `totalSize` is zero, use `rawDataSize` instead. 
When `rawDataSize` is also
    +            // zero, fall back to filesystem to get file sizes, if enabled.
    +            if (totalSize.isDefined && totalSize.get > 0L) {
    +              totalSize.get
    +            } else if (rawDataSize.isDefined && rawDataSize.get > 0L) {
    +              rawDataSize.get
    +            } else if 
(sparkSession.sessionState.conf.fallBackToHdfsForStatsEnabled) {
    +              try {
    +                val hadoopConf = sparkSession.sessionState.newHadoopConf()
    +                val fs: FileSystem = 
hiveQlTable.getPath.getFileSystem(hadoopConf)
    +                fs.getContentSummary(hiveQlTable.getPath).getLength
    +              } catch {
    +                case e: IOException =>
    +                  logWarning("Failed to get table size from hdfs.", e)
    +                  sparkSession.sessionState.conf.defaultSizeInBytes
    +              }
    +            } else {
    +              sparkSession.sessionState.conf.defaultSizeInBytes
    +            })
    +        }
    +      )
    +    }
    +  }
    +
    +  // For partitioned tables, get the size of all the partitions.
    +  // Note: the statistics might not be gathered for all the partitions.
    +  // For partial collection, we will not utilize the Hive-generated 
statistics.
    +  private def getTotalTableSize(statType: String): Option[Long] = {
    --- End diff --
    
    what if a query only reads some partitions? Looks like the table statistics 
depend on partition pruning.


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