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