[
https://issues.apache.org/jira/browse/SPARK-16699?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Qifan Pu updated SPARK-16699:
-----------------------------
Description:
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.
was:
In the following code in `VectorizedHashMapGenerator.scala`:
```
def hashBytes(b: String): String = {
val hash = ctx.freshName("hash")
val bytes = ctx.freshName("bytes")
s"""
|int $result = 0;
|byte[] $bytes = $b;
|for (int i = 0; i < $bytes.length; i++) {
| ${genComputeHash(ctx, s"$bytes[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.
> 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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