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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 35037] New: - Some Field methods use Classcast check instead of instanceof which is slow
Date Tue, 24 May 2005 07:30:38 GMT
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http://issues.apache.org/bugzilla/show_bug.cgi?id=35037

           Summary: Some Field methods use Classcast check instead of
                    instanceof which is slow
           Product: Lucene
           Version: CVS Nightly - Specify date in submission
          Platform: Other
        OS/Version: other
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Index
        AssignedTo: lucene-dev@jakarta.apache.org
        ReportedBy: psmith@apache.org


I am not sure if this is because Lucene historically needed to work with older
JVM's but with modern JVM's, instanceof is much quicker. 

The Field.stringValue(), .readerValue(), and .binaryValue() methods all use
ClassCastException checking.

Using the following test-bed class, you will see that instanceof is miles quicker:

package com.aconex.index;

public class ClassCastExceptionTest {

    private static final long ITERATIONS = 100000;

    /**
     * @param args
     */
    public static void main(String[] args) {

        runClassCastTest(1); // once for warm up
        runClassCastTest(2);
        
        runInstanceOfCheck(1);
        runInstanceOfCheck(2);

    }
    private static void runInstanceOfCheck(int run) {
        long start = System.currentTimeMillis();

        Object foo = new Foo();
        for (int i = 0; i < ITERATIONS; i++) {
            String test;
            if(foo instanceof String) {
                System.out.println("Is a string"); // should never print
            }
        }
        long end = System.currentTimeMillis();
        long diff = end - start;
        System.out.println("InstanceOf checking run #" + run + ": " + diff + "ms");
        
    }

    private static void runClassCastTest(int run) {
        long start = System.currentTimeMillis();

        Object foo = new Foo();
        for (int i = 0; i < ITERATIONS; i++) {
            String test;
            try {
                test = (String)foo;
            } catch (ClassCastException c) {
                // ignore
            }
        }
        long end = System.currentTimeMillis();
        long diff = end - start;
        System.out.println("ClassCast checking run #" + run + ": " + diff + "ms");
    }

    private static final class Foo {
    }

}


Results
=======

Run #1

ClassCast checking run #1: 1660ms
ClassCast checking run #2: 1374ms
InstanceOf checking run #1: 8ms
InstanceOf checking run #2: 4ms


Run #2
ClassCast checking run #1: 1280ms
ClassCast checking run #2: 1344ms
InstanceOf checking run #1: 7ms
InstanceOf checking run #2: 2ms


Run #3
ClassCast checking run #1: 1347ms
ClassCast checking run #2: 1250ms
InstanceOf checking run #1: 7ms
InstanceOf checking run #2: 2ms

This could explain why Documents with more Fields scales worse, as in, for lots
of Documents with lots of Fields, the effect is exacerbated.

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