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From "Raghotham Murthy (JIRA)" <>
Subject [jira] Commented: (HIVE-416) Get rid of backtrack in Hive.g
Date Fri, 17 Apr 2009 01:31:14 GMT


Raghotham Murthy commented on HIVE-416:

How about the following:

Add the production:
expr -> expr ',' expr
With this production and expr -> '(' expr ')' we can support arbitrarily nested parentheses.
The issue is that the new production will create a left-deep tree of comma-expressions. We
could implement a method which takes such a tree and flatten out comma expressions into expression

Also, I remember Venky asking for arbitrarily nested parentheses around queries for his query
authoring tool. We could do something similar and create comma-query-expressions.

> Get rid of backtrack in Hive.g
> ------------------------------
>                 Key: HIVE-416
>                 URL:
>             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-416.1.1.patch, 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
to remove the need of doing backtrack.

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