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https://issues.apache.org/jira/browse/CASSANDRA-2850?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13059589#comment-13059589
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David Allsopp commented on CASSANDRA-2850:
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I think you mean (bytes.remaining() * 2) not (bytes.remaining() / 2) - we need
twice as many chars as bytes.
Also, shouldn't byteToChar[] have length 16, not 256.
Not sure what string creation you are referring to?
I attach 2 further versions of bytesToHex (as another benchmark class 3).
Results are below (I've had to increasse the number of repeats so the stats are
significant!).
v3 uses 'normal' code and is another 20% faster for large values, and _another_
factor of 2 faster than v2, i.e. 7-10 time sfatser than the original.
v4 uses nasty reflection to avoid doing an arraycopy on the byte array - this
avoids a large chunk of memory (all the previous solutions end up doing an
arraycopy somewhere). This is now 11-13 times fatser than the original.
20M old: 1482
20M new: 360
20M v2: 249
20M v3: 203
20M v4: 125
----
old: 2137
new: 859
v2: 718
v3: 203
v4: 156
----
old: 2138
new: 843
v2: 733
v3: 188
v4: 156
----
> Converting bytes to hex string is unnecessarily slow
> ----------------------------------------------------
>
> Key: CASSANDRA-2850
> URL: https://issues.apache.org/jira/browse/CASSANDRA-2850
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Affects Versions: 0.7.6, 0.8.1
> Reporter: David Allsopp
> Priority: Minor
> Fix For: 0.8.2
>
> Attachments: 2850-v2.patch, BytesToHexBenchmark.java,
> BytesToHexBenchmark2.java, cassandra-2850a.diff
>
>
> ByteBufferUtil.bytesToHex() is unnecessarily slow - it doesn't pre-size the
> StringBuilder (so several re-sizes will be needed behind the scenes) and it
> makes quite a few method calls per byte.
> (OK, this may be a premature optimisation, but I couldn't resist, and it's a
> small change)
> Will attach patch shortly that speeds it up by about x3, plus benchmarking
> test.
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