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https://issues.apache.org/jira/browse/HADOOP-6148?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tsz Wo (Nicholas), SZE updated HADOOP-6148:
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Attachment: PureJavaCrc32.java
I think the codes could be improved a little bit as following.
{code}
public void update(byte[] b, int off, final int len) {
for(final int end = off + (len & ~3); off < end; ) {
final int c0 = crc ^ b[off++];
final int c1 = (crc >>>= 8) ^ b[off++];
final int c2 = (crc >>>= 8) ^ b[off++];
final int c3 = (crc >>>= 8) ^ b[off++];
crc = T4[c0 & 0xff] ^ T3[c1 & 0xff] ^ T2[c2 & 0xff] ^ T1[c3 & 0xff];
}
for(final int end = off + (len & 3); off < end; ) {
crc = (crc >>> 8) ^ T1[(crc ^ b[off++]) & 0xff];
}
}
{code}
PureJavaCrc32.java: I moved the codes around and did some benchmarks.
> Implement a pure Java CRC32 calculator
> --------------------------------------
>
> Key: HADOOP-6148
> URL: https://issues.apache.org/jira/browse/HADOOP-6148
> Project: Hadoop Common
> Issue Type: Improvement
> Reporter: Owen O'Malley
> Assignee: Todd Lipcon
> Attachments: benchmarks20090714.txt, crc32-results.txt,
> hadoop-5598-evil.txt, hadoop-5598-hybrid.txt, hadoop-5598.txt,
> hadoop-5598.txt, hdfs-297.txt, PureJavaCrc32.java, PureJavaCrc32.java,
> PureJavaCrc32.java, PureJavaCrc32.java, TestCrc32Performance.java,
> TestCrc32Performance.java, TestCrc32Performance.java, TestPureJavaCrc32.java
>
>
> We've seen a reducer writing 200MB to HDFS with replication = 1 spending a
> long time in crc calculation. In particular, it was spending 5 seconds in crc
> calculation out of a total of 6 for the write. I suspect that it is the
> java-jni border that is causing us grief.
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