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Date: Wed, 20 Dec 2017 23:23:01 +0000 (UTC)
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Subject: [jira] [Commented] (DRILL-5879) Optimize "Like" operator
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archived-at: Wed, 20 Dec 2017 23:23:10 -0000


    [ https://issues.apache.org/jira/browse/DRILL-5879?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16299243#comment-16299243 ] 

ASF GitHub Bot commented on DRILL-5879:
---------------------------------------

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

    https://github.com/apache/drill/pull/1072#discussion_r158159524
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/expr/fn/impl/SqlPatternContainsMatcher.java ---
    @@ -19,44 +19,283 @@
     
     import io.netty.buffer.DrillBuf;
     
    -public class SqlPatternContainsMatcher extends AbstractSqlPatternMatcher {
    +/** SQL Pattern Contains implementation */
    +public final class SqlPatternContainsMatcher extends AbstractSqlPatternMatcher {
    +  private final MatcherFcn matcherFcn;
     
       public SqlPatternContainsMatcher(String patternString) {
         super(patternString);
    +
    +    // Pattern matching is 1) a CPU intensive operation and 2) pattern and input dependent. The conclusion is
    +    // that there is no single implementation that can do it all well. So, we use multiple implementations
    +    // chosen based on the pattern length.
    +    if (patternLength == 1) {
    +      matcherFcn = new Matcher1();
    +    } else if (patternLength == 2) {
    +      matcherFcn = new Matcher2();
    +    } else if (patternLength == 3) {
    +      matcherFcn = new Matcher3();
    +    } else if (patternLength < 10) {
    +      matcherFcn = new MatcherN();
    +    } else {
    +      matcherFcn = new BoyerMooreMatcher();
    +    }
       }
     
       @Override
       public int match(int start, int end, DrillBuf drillBuf) {
    +    return matcherFcn.match(start, end, drillBuf);
    +  }
    +
    +  //--------------------------------------------------------------------------
    +  // Inner Data Structure
    +  // --------------------------------------------------------------------------
    +
    +  /** Abstract matcher class to allow us pick the most efficient implementation */
    +  private abstract class MatcherFcn {
    +    protected final byte[] patternArray;
    +
    +    protected MatcherFcn() {
    +      assert patternByteBuffer.hasArray();
    +
    +      patternArray = patternByteBuffer.array();
    +    }
    +
    +    /**
    +     * @return 1 if the pattern was matched; 0 otherwise
    +     */
    +    protected abstract int match(int start, int end, DrillBuf drillBuf);
    +  }
    +
    +  /** Handles patterns with length one */
    +  private final class Matcher1 extends MatcherFcn {
     
    -    if (patternLength == 0) { // Everything should match for null pattern string
    -      return 1;
    +    private Matcher1() {
    +      super();
         }
     
    -    final int txtLength = end - start;
    +    /** {@inheritDoc} */
    +    @Override
    +    protected final int match(int start, int end, DrillBuf drillBuf) {
    +      final int lengthToProcess = end - start;
    +      final byte firstPattByte  = patternArray[0];
     
    -    // no match if input string length is less than pattern length
    -    if (txtLength < patternLength) {
    +      // simplePattern string has meta characters i.e % and _ and escape characters removed.
    +      // so, we can just directly compare.
    +      for (int idx = 0; idx < lengthToProcess; idx++) {
    +        byte inputByte = drillBuf.getByte(start + idx);
    +
    +        if (firstPattByte != inputByte) {
    +          continue;
    +        }
    +        return 1;
    +      }
           return 0;
         }
    +  }
     
    +  /** Handles patterns with length two */
    +  private final class Matcher2 extends MatcherFcn {
     
    -    final int outerEnd = txtLength - patternLength;
    +    private Matcher2() {
    +      super();
    +    }
     
    -    outer:
    -    for (int txtIndex = 0; txtIndex <= outerEnd; txtIndex++) {
    +    /** {@inheritDoc} */
    +    @Override
    +    protected final int match(int start, int end, DrillBuf drillBuf) {
    +      final int lengthToProcess = end - start - 1;
    +      final byte firstPattByte  = patternArray[0];
    +      final byte secondPattByte = patternArray[1];
     
           // simplePattern string has meta characters i.e % and _ and escape characters removed.
           // so, we can just directly compare.
    -      for (int patternIndex = 0; patternIndex < patternLength; patternIndex++) {
    -        if (patternByteBuffer.get(patternIndex) != drillBuf.getByte(start + txtIndex + patternIndex)) {
    -          continue outer;
    +      for (int idx = 0; idx < lengthToProcess; idx++) {
    +        final byte firstInByte = drillBuf.getByte(start + idx);
    +
    +        if (firstPattByte != firstInByte) {
    +          continue;
    +        } else {
    +          final byte secondInByte = drillBuf.getByte(start + idx +1);
    +
    +          if (secondInByte == secondPattByte) {
    +            return 1;
    +          }
             }
           }
    +      return 0;
    +    }
    +  }
    +
    +  /** Handles patterns with length three */
    +  private final class Matcher3 extends MatcherFcn {
     
    -      return 1;
    +    private Matcher3() {
    +      super();
         }
     
    -    return  0;
    +    /** {@inheritDoc} */
    +    @Override
    +    protected final int match(int start, int end, DrillBuf drillBuf) {
    +      final int lengthToProcess  = end - start -2;
    +      final byte firstPattByte   = patternArray[0];
    +      final byte secondPattByte  = patternArray[1];
    +      final byte thirdPattByte   = patternArray[2];
    +
    +      // simplePattern string has meta characters i.e % and _ and escape characters removed.
    +      // so, we can just directly compare.
    +      for (int idx = 0; idx < lengthToProcess; idx++) {
    +        final byte inputByte = drillBuf.getByte(start + idx);
    +
    +        if (firstPattByte != inputByte) {
    +          continue;
    +        } else {
    +          final byte secondInByte = drillBuf.getByte(start + idx +1);
    +          final byte thirdInByte  = drillBuf.getByte(start + idx +2);
    --- End diff --
    
    Is it faster to say `secondInByte = thirdInByte`; shuffle values between variables in each iteration rather than diving into direct memory multiple types for the same byte?


> Optimize "Like" operator
> ------------------------
>
>                 Key: DRILL-5879
>                 URL: https://issues.apache.org/jira/browse/DRILL-5879
>             Project: Apache Drill
>          Issue Type: Improvement
>          Components: Execution - Relational Operators
>         Environment: * 
>            Reporter: salim achouche
>            Assignee: salim achouche
>            Priority: Minor
>             Fix For: 1.13.0
>
>
> Query: select <column-list> from <table> where colA like '%a%' or colA like '%xyz%';
> Improvement Opportunities
> # Avoid isAscii computation (full access of the input string) since we're dealing with the same column twice
> # Optimize the "contains" for-loop 
> Implementation Details
> 1)
> * Added a new integer variable "asciiMode" to the VarCharHolder class
> * The default value is -1 which indicates this info is not known
> * Otherwise this value will be set to either 1 or 0 based on the string being in ASCII mode or Unicode
> * The execution plan already shares the same VarCharHolder instance for all evaluations of the same column value
> * The asciiMode will be correctly set during the first LIKE evaluation and will be reused across other LIKE evaluations
> 2) 
> * The "Contains" LIKE operation is quite expensive as the code needs to access the input string to perform character based comparisons
> * Created 4 versions of the same for-loop to a) make the loop simpler to optimize (Vectorization) and b) minimize comparisons
> Benchmarks
> * Lineitem table 100GB
> * Query: select l_returnflag, count(*) from dfs.`<source>` where l_comment not like '%a%' or l_comment like '%the%' group by l_returnflag
> * Before changes: 33sec
> * After changes    : 27sec


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