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From Sergey Shelukhin <ser...@hortonworks.com>
Subject Re: LIKE filter pushdown for tables and partitions
Date Mon, 26 Aug 2013 21:08:46 GMT
Since there's no response I am assuming nobody cares about this code...
Jira is HIVE-5134, I will attach a patch with removal this week.

On Wed, Aug 21, 2013 at 2:28 PM, Sergey Shelukhin <sergey@hortonworks.com>wrote:

> Hi.
>
> I think there are issues with the way hive can currently do LIKE
> operator JDO pushdown and it the code should be removed for partitions
> and tables.
> Are there objections to removing LIKE from Filter.g and related areas?
> If no I will file a JIRA and do it.
>
> Details:
> There's code in metastore that is capable of pushing down LIKE
> expression into JDO for string partition keys, as well as tables.
> The code for tables doesn't appear used, and partition code definitely
> doesn't run in Hive proper because metastore client doesn't send LIKE
> expressions to server. It may be used in e.g. HCat and other places,
> but after asking some people here, I found out it probably isn't.
> I was trying to make it run and noticed some problems:
> 1) For partitions, Hive sends SQL patterns in a filter for like, e.g.
> "%foo%", whereas metastore passes them into matches() JDOQL method
> which expects Java regex.
> 2) Converting the pattern to Java regex via UDFLike method, I found
> out that not all regexes appear to work in DN. ".*foo" seems to work
> but anything complex (such as escaping the pattern using
> Pattern.quote, which UDFLike does) breaks and no longer matches
> properly.
> 3) I tried to implement common cases using JDO methods
> startsWith/endsWith/indexOf (I will file a JIRA), but when I run tests
> on Derby, they also appear to have problems with some strings (for
> example, partition with backslash in the name cannot be matched by
> LIKE "%\%" (single backslash in a string), after being converted to
> .indexOf(param) where param is "\" (escaping the backslash once again
> doesn't work either, and anyway there's no documented reason why it
> shouldn't work properly), while other characters match correctly, even
> e.g. "%".
>
> For tables, there's no SQL-like, it expects Java regex, but I am not
> convinced all Java regexes are going to work.
>
> So, I think that for future correctness sake it's better to remove this
> code.
>

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