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package org.apache.hadoop.hive.ql.stats;
import  org.apache.hadoop.conf.Configuration;

An interface for any possible implementation for gathering statistics.
public interface StatsAggregator {

This method connects to the temporary storage.

hconf HiveConf that contains the connection parameters.
true if connection is successful, false otherwise.
  public boolean connect(Configuration hconf);

This method aggregates a given statistic from all tasks (partial stats). After aggregation, this method also automatically removes all records that have been aggregated.

keyPrefix a prefix of the keys used in StatsPublisher to publish stats. Any rows that starts with the same prefix will be aggregated. For example, if the StatsPublisher uses the following compound key to publish stats: the output directory name (unique per FileSinkOperator) + the partition specs (only for dynamic partitions) + taskID (last component of task file) The keyPrefix for aggregation could be first 2 components. This will aggregates stats across all tasks for each partition.
statType a string noting the key to be published. Ex: "numRows".
a string representation of a long value, null if there are any error/exception.
  public String aggregateStats(String keyPrefixString statType);

This method closes the connection to the temporary storage.

true if close connection is successful, false otherwise.
  public boolean closeConnection();

This method clears the temporary statistics that have been published without being aggregated. Typically this happens when a job fails, or is forcibly stopped after publishing some statistics.

keyPrefix a prefix of the keys used in StatsPublisher to publish stats. It is the same as the first parameter in aggregateStats().
true if cleanup is successful, false otherwise.
  public boolean cleanUp(String keyPrefix);
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