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From "He Yongqiang (JIRA)" <>
Subject [jira] [Commented] (HIVE-2095) auto convert map join bug
Date Fri, 08 Apr 2011 05:27:05 GMT


He Yongqiang commented on HIVE-2095:

Uploading a new patch to address namit's comments.

Note, there is an existing bug in hive that cause results of auto_join29.q is not correct.

Let's file another jira for it.
basically, if the outer join filter is enabled, the query "SELECT /*+mapjoin(src1, src2)*/
* FROM src src1 RIGHT OUTER JOIN src src2 ON (src1.key = src2.key AND src1.key < 10 AND
src2.key > 10) JOIN src src3 ON (src2.key = src3.key AND src3.key < 10) SORT BY src1.key,
src1.value, src2.key, src2.value, src3.key, src3.value;" will give wrong results in today's

> auto convert map join bug
> -------------------------
>                 Key: HIVE-2095
>                 URL:
>             Project: Hive
>          Issue Type: Bug
>            Reporter: He Yongqiang
>            Assignee: He Yongqiang
>         Attachments: HIVE-2095.1.patch, HIVE-2095.2.patch
> 1) 
> when considering to choose one table as the big table candidate for a map join, if at
compile time, hive can find out that the total known size of all other tables excluding the
big table in consideration is bigger than a configured value, this big table candidate is
a bad one, and should not put into plan. Otherwise, at runtime to filter this out may cause
more time.
> 2)
> added a null check for back up tasks. Otherwise will see NullPointerException
> 3)
> CommonJoinResolver needs to know a full mapping of pathToAliases. Otherwise it will make
wrong decision.
> 4)
> changes made to the ConditionalResolverCommonJoin: added pathToAliases, aliasToSize (alias's
input size that is known at compile time, by inputSummary), and intermediate dir path.
> So the logic is, go over all the pathToAliases, and for each path, if it is from intermediate
dir path, add this path's size to all aliases. And finally based on the size information and
others like aliasToTask to choose the big table. 
> 5)
> Conditional task's children contains wrong options, which may cause join fail or incorrect
results. Basically when getting all possible children for the conditional task, should use
a whitelist of big tables. Only tables in this while list can be considered as a big table.
> Here is the logic:
> +   * Get a list of big table candidates. Only the tables in the returned set can
> +   * be used as big table in the join operation.
> +   * 
> +   * The logic here is to scan the join condition array from left to right. If
> +   * see a inner join and the bigTableCandidates is empty, add both side of this
> +   * inner join to big table candidates. If see a left outer join, and the
> +   * bigTableCandidates is empty, add the left side to it, and if the
> +   * bigTableCandidates is not empty, do nothing (which means the
> +   * bigTableCandidates is from left side). If see a right outer join, clear the
> +   * bigTableCandidates, and add right side to the bigTableCandidates, it means
> +   * the right side of a right outer join always win. If see a full outer join,
> +   * return null immediately (no one can be the big table, can not do a
> +   * mapjoin).

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