Introduce a buffered checksum for avoiding frequently calls on Checksum.update()
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Key: HADOOP-7339
URL: https://issues.apache.org/jira/browse/HADOOP-7339
Project: Hadoop Common
Issue Type: Improvement
Components: util
Reporter: Min Zhou
We found that PureJavaCRC32/CRC32.update() is the TOP 1 of the methods
consuming CPU in a map side, and in reduce side, it cost a lots of CPU too.
IFileOutputStream would frequently call Checksum.update() during writing a
record. It's very common a MR key/value less than 512 bytes. Checksum.update()
would be called every time writing a key/value.
Test case: terasort 100MB.
Checksum.update() calls has be reduced from 4030348 to 28069. This method is
not a hotspot anymore.
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