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https://issues.apache.org/jira/browse/DRILL-5697?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16133517#comment-16133517
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ASF GitHub Bot commented on DRILL-5697:
---------------------------------------

Github user paul-rogers commented on a diff in the pull request:

    https://github.com/apache/drill/pull/907#discussion_r134035974
  
    --- Diff: 
exec/java-exec/src/test/java/org/apache/drill/exec/expr/fn/impl/TestStringFunctions.java
 ---
    @@ -157,6 +157,967 @@ public void testRegexpReplace() throws Exception {
       }
     
       @Test
    +  public void testLikeStartsWith() throws Exception {
    +
    +    // all ASCII.
    +    testBuilder()
    --- End diff --
    
    The regex parsing and execution code is becoming complex. Let's test it 
with a true unit test, not just a system-level test using a query. See the test 
frameworks available. We can also discuss in person.


> Improve performance of filter operator for pattern matching
> -----------------------------------------------------------
>
>                 Key: DRILL-5697
>                 URL: https://issues.apache.org/jira/browse/DRILL-5697
>             Project: Apache Drill
>          Issue Type: Improvement
>          Components: Execution - Flow
>    Affects Versions: 1.11.0
>            Reporter: Padma Penumarthy
>            Assignee: Padma Penumarthy
>
> Queries using filter with sql like operator use Java regex library for 
> pattern matching. However, for cases like %abc (ends with abc), abc% (starts 
> with abc), %abc% (contains abc), it is observed that implementing these cases 
> with simple code instead of using regex library provides good performance 
> boost (4-6x). Idea is to use special case code for simple, common cases and 
> fall back to Java regex library for complicated ones. That will provide good 
> performance benefit for most common cases.



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