[jira] [Commented] (HIVE-21531) Vectorization: all NULL hashcodes are not computed using Murmur3

["Gopal V (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-21531?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16803607#comment-16803607 ] 

Gopal V commented on HIVE-21531:
--------------------------------

{code}
$ scala -cp ~/hw/hive/ql/target/hive-exec-3.2.0-SNAPSHOT.jar 
Picked up _JAVA_OPTIONS: -Djava.awt.headless=true -Xmx2048m
Welcome to Scala 2.11.8 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0).
Type in expressions for evaluation. Or try :help.

scala> import org.apache.hive.common.util.Murmur3;
import org.apache.hive.common.util.Murmur3

scala> import org.apache.hive.common.util.HashCodeUtil;
import org.apache.hive.common.util.HashCodeUtil

scala> val bytes = Array[Byte]('a','b','c','d');
bytes: Array[Byte] = Array(97, 98, 99, 100)

scala> HashCodeUtil.calculateBytesHashCode(bytes, 0, 4);
res0: Int = 646393889

scala> Murmur3.hash32(bytes, 0, 4, 0);
res1: Int = 1139631978

{code}

> Vectorization: all NULL hashcodes are not computed using Murmur3
> ----------------------------------------------------------------
>
>                 Key: HIVE-21531
>                 URL: https://issues.apache.org/jira/browse/HIVE-21531
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Gopal V
>            Assignee: Gopal V
>            Priority: Major
>
> The comments in Vectorized hash computation call out the MurmurHash implementation (the one using 0x5bd1e995), while the non-vectorized codepath calls out the Murmur3 one (using 0xcc9e2d51).
> The comments here are wrong
> {code}
>  /**
>    * Batch compute the hash codes for all the serialized keys.
>    *
>    * NOTE: MAJOR MAJOR ASSUMPTION:
>    *     We assume that HashCodeUtil.murmurHash produces the same result
>    *     as MurmurHash.hash with seed = 0 (the method used by ReduceSinkOperator for
>    *     UNIFORM distribution).
>    */
>   protected void computeSerializedHashCodes() {
>     int offset = 0;
>     int keyLength;
>     byte[] bytes = output.getData();
>     for (int i = 0; i < nonNullKeyCount; i++) {
>       keyLength = serializedKeyLengths[i];
>       hashCodes[i] = Murmur3.hash32(bytes, offset, keyLength, 0);
>       offset += keyLength;
>     }
>   }
> {code}
> but the wrong comment is followed in the Vector RS operator 
> {code}
>       System.arraycopy(nullKeyOutput.getData(), 0, nullBytes, 0, nullBytesLength);
>       nullKeyHashCode = HashCodeUtil.calculateBytesHashCode(nullBytes, 0, nullBytesLength);
> {code}



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