[jira] [Created] (HIVE-5144) HashTableSink allocates empty new Object[] arrays & OOMs - use a static emptyRow instead

["Gopal V (JIRA)" <ji...@apache.org>]

Gopal V created HIVE-5144:
-----------------------------

             Summary: HashTableSink allocates empty new Object[] arrays & OOMs - use a static emptyRow instead
                 Key: HIVE-5144
                 URL: https://issues.apache.org/jira/browse/HIVE-5144
             Project: Hive
          Issue Type: Bug
          Components: Query Processor
         Environment: Ubuntu LXC + -Xmx4096m client opts
            Reporter: Gopal V
            Assignee: Gopal V
            Priority: Minor


The map-join hashtable sink in the local-task creates an in-memory hashtable with the following code.

{code}
 Object[] value = JoinUtil.computeMapJoinValues(row, joinValues[alias],
...
 MapJoinRowContainer rowContainer = tableContainer.get(key);
    if (rowContainer == null) {
      rowContainer = new MapJoinRowContainer();
      rowContainer.add(value);
{code}

But for a query where the joinValues[alias].size() == 0, this results in a large number of unnecessary allocations which would be better served with a copy-on-write default value container & a pre-allocated zero object array which is immutable (the only immutable array there is in java).

The query tested is roughly the following to scan all of customer_demographics in the hash-sink

{code}

select c_salutation, count(1)
 from customer
      JOIN customer_demographics ON customer.c_current_cdemo_sk = customer_demographics.cd_demo_sk
 group by c_salutation
 limit 10
;

{code}

When running with current trunk, the code results in an OOM with 512Mb ram.

{code}
2013-08-23 05:11:26	Processing rows:	1400000	Hashtable size:	1399999	Memory usage:	292418944	percentage:	0.579

Execution failed with exit status: 3
Obtaining error information
{code}



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