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

["Ashutosh Chauhan (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-5144?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13748839#comment-13748839 ] 

Ashutosh Chauhan commented on HIVE-5144:
----------------------------------------

Nice findings, Gopal!

Couple of comments:
* Shall we do initialization of empty row and container in the constructor?
* Also mark these fields as transient.
                
> 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 + -Xmx512m client opts
>            Reporter: Gopal V
>            Assignee: Gopal V
>            Priority: Minor
>              Labels: perfomance
>         Attachments: HIVE-5144.01.patch
>
>
> 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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