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https://issues.apache.org/jira/browse/HIVE-279?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12677548#action_12677548
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Namit Jain commented on HIVE-279:
---------------------------------
Some high level comments:
1. Add more comments everywhere, specifically in joinPPD (OpProcFactory)
2. Remove operator specific code in ExprWalkerProcFactory: ColumnExprProcessor:
process
3. Use specific data-structures where-ever possible instead of using more
generic data-structures.
ExprWalkerInfo:
private Map<String, List<Node>> pushdownPreds;
private Map<Node, ExprInfo> exprInfoMap;
In both of them, Node means exprNodeDesc, why dont we use that instead ?
Simlarly, in OpWalkerInfo:
private Map<Node, ExprWalkerInfo> opToPrunedPredsMap;
private Map<Operator<? extends Serializable>, OpParseContext> opToParseCtxMap;
use Operator instead of Node in opToPrunedPredsMap
4. Can you move OpWalker and ExprWalker in different directories ?
5. Why are filters only pushed on top of TableScan - cant it be done anywhere.
- If you want to do so in a follow-up, can you file a JIRA for that ?
6. No apache header in many files (ppd directory)
SemanticAnalyzer.java:
A comment explaining the reason for existence of colInfoMap will help. Give an
example: group by
where the table column order is different from the grouped column order.
Same for posAliasMap, nameToInputColumnInfoMap for JOIN
genJoinOperatorChildren:
if(aliases == null) {
aliases = new HashSet<String>();
posToAliasMap.put(pos, aliases);
}
isn't the IF redundant ?
> Implement predicate push down for hive queries
> ----------------------------------------------
>
> Key: HIVE-279
> URL: https://issues.apache.org/jira/browse/HIVE-279
> Project: Hadoop Hive
> Issue Type: New Feature
> Affects Versions: 0.2.0
> Reporter: Prasad Chakka
> Assignee: Prasad Chakka
> Attachments: hive-279.2.patch, hive-279.patch
>
>
> Push predicates that are expressed in outer queries into inner queries where
> possible so that rows will get filtered out sooner.
> eg.
> select a.*, b.* from a join b on (a.uid = b.uid) where a.age = 20 and
> a.gender = 'm'
> current compiler generates the filter predicate in the reducer after the join
> so all the rows have to be passed from mapper to reducer. by pushing the
> filter predicate to the mapper, query performance should improve.
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