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https://issues.apache.org/jira/browse/HIVE-19501?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16472944#comment-16472944
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Gopal V commented on HIVE-19501:
--------------------------------
FYI, the murmur64 for Long is actually pretty trivial.
{code}
public static long hash64(long data) {
long hash = DEFAULT_SEED;
long k = Long.reverseBytes(data);
int length = Long.BYTES;
// mix functions
k *= C1;
k = Long.rotateLeft(k, R1);
k *= C2;
hash ^= k;
hash = Long.rotateLeft(hash, R2) * M + N1;
// finalization
hash ^= length;
hash = fmix64(hash);
return hash;
}
{code}
and does not need a byte[] array.
> Fix HyperLogLog to be threadsafe
> --------------------------------
>
> Key: HIVE-19501
> URL: https://issues.apache.org/jira/browse/HIVE-19501
> Project: Hive
> Issue Type: Bug
> Reporter: Zoltan Haindrich
> Priority: Major
>
> not sure if this is an issue in reality or not; but there are 3 static fields
> in HyperLogLog which are rewritten during working; if there are multiple
> threads are calculating HLL in the same JVM, there is a theoretical chance
> that they might overwrite eachothers value...
> static fields:
> https://github.com/apache/hive/blob/8028ce8a4cf5a03e2998c33e032a511fae770b47/standalone-metastore/src/main/java/org/apache/hadoop/hive/common/ndv/hll/HyperLogLog.java#L65
> usage:
> https://github.com/apache/hive/blob/8028ce8a4cf5a03e2998c33e032a511fae770b47/standalone-metastore/src/main/java/org/apache/hadoop/hive/common/ndv/hll/HyperLogLog.java#L216
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