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From "Ashutosh Chauhan (JIRA)" <>
Subject [jira] [Updated] (HIVE-4548) Speed up vectorized LIKE filter for special cases abc%, %abc and %abc%
Date Mon, 01 Jul 2013 22:25:20 GMT


Ashutosh Chauhan updated HIVE-4548:

    Resolution: Fixed
        Status: Resolved  (was: Patch Available)

Committed to branch. Thanks, Teddy!
> Speed up vectorized LIKE filter for special cases abc%, %abc and %abc%
> ----------------------------------------------------------------------
>                 Key: HIVE-4548
>                 URL:
>             Project: Hive
>          Issue Type: Sub-task
>    Affects Versions: vectorization-branch
>            Reporter: Eric Hanson
>            Assignee: Teddy Choi
>            Priority: Minor
>             Fix For: vectorization-branch
>         Attachments: HIVE-4548.1-with-benchmark.patch.txt, HIVE-4548.1-without-benchmark.patch.txt,
HIVE-4548.2-with-benchmark.patch.txt, HIVE-4548.2-without-benchmark.patch.txt, HIVE-4548.3.with-benchmark.patch.txt,
> Speed up vectorized LIKE filter evaluation for abc%, %abc, and %abc% pattern special
cases (here, abc is just a place holder for some fixed string).  
> Problem: The current vectorized LIKE implementation always calls the standard LIKE function
code in But this is pretty expensive. It calls multiple functions and allocates
at least one new object per call. Probably 80% of uses of LIKE are for the simple patterns
abc%, %abc, and %abc%.  These can be implemented much more efficiently.
> Start by speeding up the case for  
>     Column LIKE "abc%"
> The goal would be to minimize expense in the inner loop. Don't use new() in the inner
loop, and write a static function that checks the prefix of the string matches the like pattern
as efficiently as possible, operating directly on the byte array holding UTF-8-encoded string
data, and avoiding unnecessary additional function calls and if/else logic. Call that in the
inner loop.
> If feasible, consider using a template-driven approach, with an instance of the template
expanded for each of the three cases. Start doing the abc% (prefix match) by hand, then consider
templatizing for the other two cases.
> The code is in the "vectorization" branch of the main hive repo.
> Start by checking in the constructor for if the
pattern is one of the simple special cases. If so, record that, and have the evaluate() method
call a special-case function for each case, i.e. the general case, and each of the 3 special
cases. All the dynamic decision-making would be done once per vector, not once per element.

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