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From Sergey Shelukhin <ser...@hortonworks.com>
Subject Re: LIKE filter pushdown for tables and partitions
Date Tue, 27 Aug 2013 02:48:56 GMT
Adding user list. Any objections to removing LIKE support from
getPartitionsByFilter?

On Mon, Aug 26, 2013 at 2:54 PM, Ashutosh Chauhan <hashutosh@apache.org>wrote:

> Couple of questions:
>
> 1. What about LIKE operator for Hive itself? Will that continue to work
> (presumably because there is an alternative path for that).
> 2. This will nonetheless break other direct consumers of metastore client
> api (like HCatalog).
>
> I see your point that we have a buggy implementation, so whats out there is
> not safe to use. Question than really is shall we remove this code, thereby
> breaking people for whom current buggy implementation is good enough (or
> you can say salvage them from breaking in future). Or shall we try to fix
> it now?
> My take is if there are no users of this anyways, then there is no point
> fixing it for non-existing users, but if there are we probably have to. I
> will suggest you to send an email to users@hive to ask if there are users
> for this.
>
> Thanks,
> Ashutosh
>
>
>
> On Mon, Aug 26, 2013 at 2:08 PM, Sergey Shelukhin <sergey@hortonworks.com
> >wrote:
>
> > 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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> >
>

-- 
CONFIDENTIALITY NOTICE
NOTICE: This message is intended for the use of the individual or entity to 
which it is addressed and may contain information that is confidential, 
privileged and exempt from disclosure under applicable law. If the reader 
of this message is not the intended recipient, you are hereby notified that 
any printing, copying, dissemination, distribution, disclosure or 
forwarding of this communication is strictly prohibited. If you have 
received this communication in error, please contact the sender immediately 
and delete it from your system. Thank You.

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