Thomas Heigl created WICKET-6771:
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Summary: Performance issues accessing component metadata
Key: WICKET-6771
URL: https://issues.apache.org/jira/browse/WICKET-6771
Project: Wicket
Issue Type: Bug
Components: wicket-core
Affects Versions: 9.0.0-M5, 8.7.0
Reporter: Thomas Heigl
Attachments: image-2020-04-27-09-57-20-368.png
We have recently rolled out continuous profiling using JFR to our production
environment. With some very surprising results. The biggest one being that one
of the hottest methods in our application is {{Component.getMetaData():}}
!image-2020-04-27-09-57-20-368.png|width=1143,height=745!
Component metadata is used to store removal operations for the duration of the
request and is accessed every time a component's children are iterated and when
detaching components.
The profiler screenshot above shows one of the possible code paths.
I couldn't believe this at first so I decided to write a JMH benchmark. It
turns out that between 20% and 35% of time in the detach method is spent on
getting (empty) removal metadata.
The benchmark compares checking metadata with a request-level boolean flag that
is set when a component has removals:
{quote}# Run complete. Total time: 00:02:44
Benchmark Score Error Units
ComponentBenchmarks.detachComponentWithFlags *12295,363* ± 71,343 ops/s
ComponentBenchmarks.detachComponentWithMetaData *8855,321* ± 34,743 ops/s
{quote}
I will shortly create a PR with the benchmark so you can replicate these issues.
I have not found time yet to profile the metadata code to get to the root cause
of this. Help would be greatly appreciated. If we cannot improve the
performance of accessing metadata, I'd suggest introducing request-level flags
that are checked before accessing metadata for the most active code paths like
I have done in the benchmark.
I will create separate tickets for some other issues found by profiling on
production that are quite easy to fix. This issue is the most important finding
though.
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