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https://issues.apache.org/jira/browse/HADOOP-6884?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Doug Cutting updated HADOOP-6884:
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Attachment: FunAgain.java
You've benchmarked a case that isn't in the existing patch (3 variables) and
certainly isn't typical. Your 'static' case still boxes.
So your benchmark mostly shows that boxing costs, and string concatenation
costs even more yet. I don't see how it shows that any of these costs are
significant in the Hadoop codebase.
I've attached a version that benchmarks the more typical single-parameter using
slf4j and a static version that avoids boxing.
The output this gives is:
java.version = 1.6.0_20
java.runtime.name = Java(TM) SE Runtime Environment
java.runtime.version = 1.6.0_20-b02
java.vm.version = 16.3-b01
java.vm.vendor = Sun Microsystems Inc.
java.vm.name = Java HotSpot(TM) Server VM
java.vm.specification.version = 1.0
java.specification.version = 1.6
os.arch = i386
os.name = Linux
os.version = 2.6.32-24-generic-pae
n=10000000
LOG.isDebugEnabled(): 13 ms
static debug(..) : 78 ms
LOG.debug(..) : 472 ms
What does this show? It shows that simply switching to slf4j using format
strings would remove string concatenation costs speeding log statements by
around 10x without any bloat. It does not show whether that improvement would
be significant in any larger Hadoop benchmark, but at least the cost in code
readability would be null. Further it shows that, if we find that logging
costs are significant somewhere due to boxing, we could optimize that with
static methods, gaining another 5x without losing any readability. Finally, if
we find that logging costs are still somewhere significant, we can improve them
yet another 6x with some impairment to readability. This is a bit like manual
loop unrolling. We'll do it in certain performance-critical areas when it's
shown to provide a significant advantage, but we shouldn't do it blindly for
every loop.
> Add LOG.isDebugEnabled() guard for each LOG.debug("...")
> --------------------------------------------------------
>
> Key: HADOOP-6884
> URL: https://issues.apache.org/jira/browse/HADOOP-6884
> Project: Hadoop Common
> Issue Type: Improvement
> Affects Versions: 0.22.0
> Reporter: Erik Steffl
> Assignee: Erik Steffl
> Fix For: 0.22.0
>
> Attachments: FunAgain.java, FunAgain.java, HADOOP-6884-0.22-1.patch,
> HADOOP-6884-0.22.patch
>
>
> Each LOG.debug("...") should be executed only if LOG.isDebugEnabled() is
> true, in some cases it's expensive to construct the string that is being
> printed to log. It's much easier to always use LOG.isDebugEnabled() because
> it's easier to check (rather than in each case reason whether it's necessary
> or not).
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