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https://issues.apache.org/jira/browse/HIVE-416?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Zheng Shao updated HIVE-416:
----------------------------
Attachment: HIVE-416.1.patch
This patch changed Hive.g to disable backtrack.
All ambiguity are resolved except an unresolvable one: "Identifier DOT
Identifier". This one will require some work in the SemanticAnalyzer as well.
We had to add a little restriction to the grammar:
1. "SELECT TRANSFORM" will have to have brackets around all expression List
after it. Originally the brackets are optional;
2. "MAP" and "REDUCE" cannot have brackets around all expression list after it
(just like SELECT). Originally we allow optional brackets.
Both changes are required if we want to disable backtrack.
> Get rid of backtrack in Hive.g
> ------------------------------
>
> Key: HIVE-416
> URL: https://issues.apache.org/jira/browse/HIVE-416
> Project: Hadoop Hive
> Issue Type: Improvement
> Components: Query Processor
> Affects Versions: 0.4.0
> Reporter: Zheng Shao
> Assignee: Zheng Shao
> Fix For: 0.4.0
>
> Attachments: HIVE-416.1.patch
>
>
> Hive.g now still uses "backtrack=true". "backtrack" not only slows down the
> parsing in case of error, it can also produce wrong syntax error messages
> (usually based on the last try of the backtracking).
> We should follow
> http://www.antlr.org/wiki/display/ANTLR3/How+to+remove+global+backtracking+from+your+grammar
> to remove the need of doing backtrack.
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