[
https://issues.apache.org/jira/browse/HIVE-22294?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Qiang.Kang reassigned HIVE-22294:
---------------------------------
Assignee: Rui Li
> ConditionalWork cannot be cast to MapredWork When both skew.join and
> auto.convert is on.
> -------------------------------------------------------------------------------------------
>
> Key: HIVE-22294
> URL: https://issues.apache.org/jira/browse/HIVE-22294
> Project: Hive
> Issue Type: Bug
> Components: Physical Optimizer
> Affects Versions: 2.3.0, 3.1.1, 2.3.4
> Reporter: Qiang.Kang
> Assignee: Rui Li
> Priority: Critical
>
> Our hive version is 1.2.1 which has merged some patches (including patches
> mentioned in https://issues.apache.org/jira/browse/HIVE-14557,
> https://issues.apache.org/jira/browse/HIVE-16155 ) .
>
> My sql query string is like this:
> ```
> set hive.auto.convert.join = true;
> set hive.optimize.skewjoin=true;
>
> SELECT a.*
> FROM
> a
> JOIN b
> ON a.id=b.id AND a.uid = b.uid
> LEFT JOIN c
> ON b.id=c.id AND b.uid=c.uid;
> ```
> And we met some error:
> FAILED: ClassCastException org.apache.hadoop.hive.ql.plan.ConditionalWork
> cannot be cast to org.apache.hadoop.hive.ql.plan.MapredWork
>
> The main reason is that there is a conditional task (*MapJoin*) in the list
> tasks of another Conditional task (*SkewJoin*). Here is the code snippet
> where it throws this exception:
> `org.apache.hadoop.hive.ql.optimizer.physical.MapJoinResolver:`
> ```java
> public Object dispatch(Node nd, Stack<Node> stack, Object... nodeOutputs)
> throws SemanticException {
> Task<? extends Serializable> currTask = (Task<? extends Serializable>) nd;
> // not map reduce task or not conditional task, just skip
> if (currTask.isMapRedTask()) {
> if (currTask instanceof ConditionalTask) {
> // get the list of task
> List<Task<? extends Serializable>> taskList = ((ConditionalTask)
> currTask).getListTasks();
> for (Task<? extends Serializable> tsk : taskList) {
> if (tsk.isMapRedTask()) {
>
> // ATTENTION: tsk May be ConditionalTask !!!
> this.processCurrentTask(tsk, ((ConditionalTask) currTask));
> }
> }
> } else {
> this.processCurrentTask(currTask, null);
> }
> }
> return null;
> }
> private void processCurrentTask(Task<? extends Serializable> currTask,
> ConditionalTask conditionalTask) throws SemanticException {
> // get current mapred work and its local work
> MapredWork mapredWork = (MapredWork) currTask.getWork(); // WRONG!!!!!!
> MapredLocalWork localwork = mapredWork.getMapWork().getMapRedLocalWork();
> ```
>
> Here is some detail Information about query plan:
> *- set hive.auto.convert.join = true; set hive.optimize.skewjoin=false;*
> ```
> Stage-1 is a root stage [a join b]
> Stage-12 [map join]depends on stages: Stage-1 , consists of Stage-13, Stage-2
> Stage-13 has a backup stage: Stage-2
> Stage-11 depends on stages: Stage-13
> Stage-8 depends on stages: Stage-2, Stage-11 , consists of Stage-5, Stage-4,
> Stage-6
> Stage-5
> Stage-0 depends on stages: Stage-5, Stage-4, Stage-7
> Stage-14 depends on stages: Stage-0
> Stage-3 depends on stages: Stage-14
> Stage-4
> Stage-6
> Stage-7 depends on stages: Stage-6
> Stage-2
> ```
> *- set hive.auto.convert.join = false; set hive.optimize.skewjoin=true;*
> ```
> STAGE DEPENDENCIES:
> Stage-1 is a root stage
> Stage-12 depends on stages: Stage-1 , consists of Stage-13, Stage-2
> Stage-13 [skew Join map local task]
> Stage-11 depends on stages: Stage-13
> Stage-2 depends on stages: Stage-11
> Stage-8 depends on stages: Stage-2 , consists of Stage-5, Stage-4, Stage-6
> Stage-5
> Stage-0 depends on stages: Stage-5, Stage-4, Stage-7
> Stage-14 depends on stages: Stage-0
> Stage-3 depends on stages: Stage-14
> Stage-4
> Stage-6
> Stage-7 depends on stages: Stage-6
> ```
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