[jira] [Commented] (SPARK-16699) Fix performance bug in hash aggregate on long string keys
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https://issues.apache.org/jira/browse/SPARK-16699?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15391239#comment-15391239
]
Dongjoon Hyun commented on SPARK-16699:
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Hi, [~qifan].
Nice catch! By the way, usually, only committers set `FIX VERSION` field.
You had better leave it blank next time. :)
> Fix performance bug in hash aggregate on long string keys
> -
>
> Key: SPARK-16699
> URL: https://issues.apache.org/jira/browse/SPARK-16699
> Project: Spark
> Issue Type: Bug
> Components: Spark Core
>Affects Versions: 2.0.0
>Reporter: Qifan Pu
> Fix For: 2.0.0
>
>
> In the following code in `VectorizedHashMapGenerator.scala`:
> ```
> def hashBytes(b: String): String = {
> val hash = ctx.freshName("hash")
> s"""
> |int $result = 0;
> |for (int i = 0; i < $b.length; i++) {
> | ${genComputeHash(ctx, s"$b[i]", ByteType, hash)}
> | $result = ($result ^ (0x9e3779b9)) + $hash + ($result << 6) +
> ($result >>> 2);
> |}
>""".stripMargin
> }
> ```
> when b=input.getBytes(), the current 2.0 code results in getBytes() being
> called n times, n being length of input. getBytes() involves memory copy is
> thus expensive and causes a performance degradation.
> Fix is to evaluate getBytes() before the for loop.
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[jira] [Commented] (SPARK-16699) Fix performance bug in hash aggregate on long string keys
[
https://issues.apache.org/jira/browse/SPARK-16699?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15391191#comment-15391191
]
Apache Spark commented on SPARK-16699:
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User 'ooq' has created a pull request for this issue:
https://github.com/apache/spark/pull/14337
> Fix performance bug in hash aggregate on long string keys
> -
>
> Key: SPARK-16699
> URL: https://issues.apache.org/jira/browse/SPARK-16699
> Project: Spark
> Issue Type: Bug
> Components: Spark Core
>Affects Versions: 2.0.0
>Reporter: Qifan Pu
> Fix For: 2.0.0
>
>
> In the following code in `VectorizedHashMapGenerator.scala`:
> ```
> def hashBytes(b: String): String = {
> val hash = ctx.freshName("hash")
> s"""
> |int $result = 0;
> |for (int i = 0; i < $b.length; i++) {
> | ${genComputeHash(ctx, s"$b[i]", ByteType, hash)}
> | $result = ($result ^ (0x9e3779b9)) + $hash + ($result << 6) +
> ($result >>> 2);
> |}
>""".stripMargin
> }
> ```
> when b=input.getBytes(), the current 2.0 code results in getBytes() being
> called n times, n being length of input. getBytes() involves memory copy is
> thus expensive and causes a performance degradation.
> Fix is to evaluate getBytes() before the for loop.
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