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https://issues.apache.org/jira/browse/LOG4J2-753?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Remko Popma resolved LOG4J2-753.
--------------------------------
Resolution: Fixed
Fix Version/s: 2.1
CachedClock assumes that some of the "jumps" or gaps in the timestamp are
caused by the updater background thread being starved. It tries to reduce the
timestamp gaps by forcing regular timestamp updates on the caller thread.
This was implemented with a volatile field, and updating this field with every
call itself became a source of contention.
Removing the volatile keyword improved the performance considerably. This
removes the restriction that every thread's update must be visible to all other
threads, so the caches no longer need to be synchronized on every call,
reducing the inter-cache traffic.
Benchmark results:
*8 threads*
{code}
java -jar log4j-perf\target\microbenchmarks.jar ".*ClocksBen.*" -t 8 -f 1 -wi
10 -i 10
Benchmark Mode Samples
Mean Mean error Units
o.a.l.l.p.j.ClocksBenchmark.baseline sample 560304
22.958 0.601 ns/op
o.a.l.l.p.j.ClocksBenchmark.coarseCachedClock sample 550280
23.972 0.649 ns/op
o.a.l.l.p.j.ClocksBenchmark.systemClock sample 550963
157.133 270.416 ns/op
o.a.l.l.p.j.ClocksBenchmark.cachedClock sample 715130
204.227 258.307 ns/op
o.a.l.l.p.j.ClocksBenchmark.oldCachedClock sample 537132
306.809 452.187 ns/op
{code}
*1 thread*
{code}
java -jar log4j-perf\target\microbenchmarks.jar ".*ClocksBen.*" -t 1 -f 1 -wi
10 -i 10
Benchmark Mode Samples
Mean Mean error Units
o.a.l.l.p.j.ClocksBenchmark.baseline sample 146712
18.105 0.897 ns/op
o.a.l.l.p.j.ClocksBenchmark.coarseCachedClock sample 115812
20.075 1.049 ns/op
o.a.l.l.p.j.ClocksBenchmark.systemClock sample 134645
20.540 1.002 ns/op
o.a.l.l.p.j.ClocksBenchmark.cachedClock sample 162196
20.189 1.000 ns/op
o.a.l.l.p.j.ClocksBenchmark.oldCachedClock sample 96522
45.996 1.707 ns/o
{code}
> CachedClock performs badly when contended by many threads
> ---------------------------------------------------------
>
> Key: LOG4J2-753
> URL: https://issues.apache.org/jira/browse/LOG4J2-753
> Project: Log4j 2
> Issue Type: Improvement
> Components: Core
> Affects Versions: 2.0
> Reporter: Remko Popma
> Assignee: Remko Popma
> Fix For: 2.1
>
>
> See LOG4J2-744 comments for JMH benchmarks highlighting the issue.
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