Gang Deng created HIVE-3420:
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Summary: Inefficiency in hbase handler when process query
including rowkey range scan
Key: HIVE-3420
URL: https://issues.apache.org/jira/browse/HIVE-3420
Project: Hive
Issue Type: Improvement
Components: HBase Handler
Affects Versions: 0.9.0
Environment: Hive-0.9.0 + HBase-0.94.1
Reporter: Gang Deng
Priority: Critical
When query hive with hbase rowkey range, hive map tasks do not leverage
startrow, endrow information in tablesplit. For example, if the rowkeys fit
into 5 hbase files, then where will be 5 map tasks. Ideally, each task will
process 1 file. But in current implementation, each task processes 5 files
repeatedly. The behavior not only waste network bandwidth, but also worse the
lock contention in HBase block cache as each task have to access the same
block. The problem code is in HiveHBaseTableInputFormat.convertFilte as below:
……
if (tableSplit != null) {
tableSplit = new TableSplit(
tableSplit.getTableName(),
startRow,
stopRow,
tableSplit.getRegionLocation());
}
scan.setStartRow(startRow);
scan.setStopRow(stopRow);
……
As tableSplit already include startRow, endRow information of file, the better
implementation will be:
……
byte[] splitStart = startRow;
byte[] splitStop = stopRow;
if (tableSplit != null) {
if(tableSplit.getStartRow() != null){
splitStart = startRow.length == 0 ||
Bytes.compareTo(tableSplit.getStartRow(), startRow) >= 0 ?
tableSplit.getStartRow() : startRow;
}
if(tableSplit.getEndRow() != null){
splitStop = (stopRow.length == 0 ||
Bytes.compareTo(tableSplit.getEndRow(), stopRow) <= 0) &&
tableSplit.getEndRow().length > 0 ?
tableSplit.getEndRow() : stopRow;
}
tableSplit = new TableSplit(
tableSplit.getTableName(),
splitStart,
splitStop,
tableSplit.getRegionLocation());
}
scan.setStartRow(splitStart);
scan.setStopRow(splitStop);
……
In my test, the changed code will improve performance more than 30%.
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