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From "Sun Rui (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-5891) Alias conflict when merging multiple mapjoin tasks into their common child mapred task
Date Thu, 19 Dec 2013 13:40:08 GMT

    [ https://issues.apache.org/jira/browse/HIVE-5891?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13852894#comment-13852894
] 

Sun Rui commented on HIVE-5891:
-------------------------------

[~yhuai] Thanks for your comments:)
It seems there is no quick way to get the correct QB for a join operator. However, since QBJoinTree's
id is same as it's QB's id, we can just use QBJoinTree's id as QB's id. I found simliar usages
in the HIVE code base.

I note that something wrong in my first patch. parseCtx.getJoinContext() is used to map the
join operator to its QBJoinTree, but this is not enough. A join operator may be a MapJoin
or SMBJoin operator instead of a common join operator, so parseCtx.getMapJoinContext() and
parseCtx.getSmbMapJoinContext() should also be checked.

I have another thought. Maybe we can define a method in GenMapRedUtils. On each invokation,
this method returns a unique intermediate name. Thus we don't have to use QB's id.

What's your opinion?

> Alias conflict when merging multiple mapjoin tasks into their common child mapred task
> --------------------------------------------------------------------------------------
>
>                 Key: HIVE-5891
>                 URL: https://issues.apache.org/jira/browse/HIVE-5891
>             Project: Hive
>          Issue Type: Bug
>          Components: Query Processor
>    Affects Versions: 0.12.0
>            Reporter: Sun Rui
>            Assignee: Sun Rui
>         Attachments: HIVE-5891.1.patch
>
>
> Use the following test case with HIVE 0.12:
> {code:sql}
> create table src(key int, value string);
> load data local inpath 'src/data/files/kv1.txt' overwrite into table src;
> select * from (
>   select c.key from
>     (select a.key from src a join src b on a.key=b.key group by a.key) tmp
>     join src c on tmp.key=c.key
>   union all
>   select c.key from
>     (select a.key from src a join src b on a.key=b.key group by a.key) tmp
>     join src c on tmp.key=c.key
> ) x;
> {code}
> We will get a NullPointerException from Union Operator:
> {noformat}
> java.lang.RuntimeException: org.apache.hadoop.hive.ql.metadata.HiveException: Hive Runtime
Error while processing row {"_col0":0}
> 	at org.apache.hadoop.hive.ql.exec.mr.ExecMapper.map(ExecMapper.java:175)
> 	at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:50)
> 	at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:436)
> 	at org.apache.hadoop.mapred.MapTask.run(MapTask.java:372)
> 	at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:212)
> Caused by: org.apache.hadoop.hive.ql.metadata.HiveException: Hive Runtime Error while
processing row {"_col0":0}
> 	at org.apache.hadoop.hive.ql.exec.MapOperator.process(MapOperator.java:544)
> 	at org.apache.hadoop.hive.ql.exec.mr.ExecMapper.map(ExecMapper.java:157)
> 	... 4 more
> Caused by: java.lang.NullPointerException
> 	at org.apache.hadoop.hive.ql.exec.UnionOperator.processOp(UnionOperator.java:120)
> 	at org.apache.hadoop.hive.ql.exec.Operator.process(Operator.java:504)
> 	at org.apache.hadoop.hive.ql.exec.Operator.forward(Operator.java:842)
> 	at org.apache.hadoop.hive.ql.exec.SelectOperator.processOp(SelectOperator.java:88)
> 	at org.apache.hadoop.hive.ql.exec.Operator.process(Operator.java:504)
> 	at org.apache.hadoop.hive.ql.exec.Operator.forward(Operator.java:842)
> 	at org.apache.hadoop.hive.ql.exec.CommonJoinOperator.genUniqueJoinObject(CommonJoinOperator.java:652)
> 	at org.apache.hadoop.hive.ql.exec.CommonJoinOperator.genUniqueJoinObject(CommonJoinOperator.java:655)
> 	at org.apache.hadoop.hive.ql.exec.CommonJoinOperator.checkAndGenObject(CommonJoinOperator.java:758)
> 	at org.apache.hadoop.hive.ql.exec.MapJoinOperator.processOp(MapJoinOperator.java:220)
> 	at org.apache.hadoop.hive.ql.exec.Operator.process(Operator.java:504)
> 	at org.apache.hadoop.hive.ql.exec.Operator.forward(Operator.java:842)
> 	at org.apache.hadoop.hive.ql.exec.TableScanOperator.processOp(TableScanOperator.java:91)
> 	at org.apache.hadoop.hive.ql.exec.Operator.process(Operator.java:504)
> 	at org.apache.hadoop.hive.ql.exec.Operator.forward(Operator.java:842)
> 	at org.apache.hadoop.hive.ql.exec.MapOperator.process(MapOperator.java:534)
> 	... 5 more
> {noformat}
>   
> The root cause is in CommonJoinTaskDispatcher.mergeMapJoinTaskIntoItsChildMapRedTask().
> {noformat}
>   +--------------+      +--------------+
>   | MapJoin task |      | MapJoin task |
>   +--------------+      +--------------+
>              \             /
>               \           /
>              +--------------+
>              |  Union task  |
>              +--------------+
> {noformat}             
> CommonJoinTaskDispatcher merges the two MapJoin tasks into their common child: Union
task. The two MapJoin tasks have the same alias name for their big tables: $INTNAME, which
is the name of the temporary table of a join stream. The aliasToWork map uses alias as key,
so eventually only the MapJoin operator tree of one MapJoin task is saved into the aliasToWork
map of the Union task, while the MapJoin operator tree of another MapJoin task is lost. As
a result, Union operator won't be initialized because not all of its parents gets intialized
(The Union operator itself indicates it has two parents, but actually it has only 1 parent
because another parent is lost).
> This issue does not exist in HIVE 0.11 and thus is a regression bug in HIVE 0.12.
> The propsed solution is to use the query ID as prefix for the join stream name to avoid
conflict and add sanity check code in CommonJoinTaskDispatcher that merge of a MapJoin task
into its child MapRed task is skipped if there is any alias conflict. Please review the patch.
I am not sure if the patch properly handles the case of DemuxOperator.
> BTW, anyone knows the origin of "$INTNAME"? it is so confusing, maybe we can replace
it with a meaningful name.



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