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From "Zheng Shao (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HIVE-416) Get rid of backtrack in Hive.g
Date Wed, 15 Apr 2009 22:15:14 GMT

     [ https://issues.apache.org/jira/browse/HIVE-416?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

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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