RFR: 8185525: [Event Request] Add Tracing event for DictionarySizes

[Erik Gahlin]

Hi Gerard,

Here are some comments about the metadata (to make it consistent with 
other events).

The events should not be in the "Java Application" category since they 
are JVM events. You could perhaps put them in "Java Virtual Machine, 
Runtime, Tables". Some comments about the names and labels of fields.

- Label: Number of buckets => Bucket Count
- Label: Number of entries => Entry Count
- Label: Total footprint => Total Footprint

Could you remove descriptions that are exactly the same as the label.

- Label: Maximum bucket size => Maximum Bucket Size
- Label: Average bucket size => Average Bucket Size
- Label: Variance of bucket  size => Bucket Size Variance
- Name: stdDevOfBucketSize => bucketSizeStandardDeviation
- Label: Standard deviation of bucket size => Bucket Size Standard 
Deviation"

Instead of using the word "size", it may make more sense to use the word 
"count" here as well, i.e "Average Bucket Count", or maybe I'm missing 
something? Is there a difference?

I wonder how useful standard deviation and variance is? If support 
engineers are looking at a recording, or JMC adds a rule for the events, 
what would a good or bad value be? Is it possible to use the information 
for troubleshooting?

- Name: addRate => insertionRate
- Label: Rate of addition =>  Insertation Rate
- Name: removeRate => removalRate
- Label: Rate of removal => Removal Rate

I'm missing unit tests for the events. Could you please add in 
/test/jdk/jdk/jfr/event/runtime. They can be sanity tests. i.e the 
average not exceeding max, no negative values etc.

Thanks!
Erik

> Hi all,
>
> Please review this feature, which adds tracing events for the internal 
> hash tables.
>
> The following attributes are implemented:
>
> <Field type="ulong" name="numberOfBuckets" label="Number of buckets" 
> description="Number of buckets" />
> <Field type="ulong" name="numberOfEntries" label="Number of entries" 
> description="Number of all entries" />
> <Field type="ulong" contentType="bytes" name="totalFootprint" 
> label="Total footprint" description="Total memory footprint (the table 
> itself plus all of the entries)" />
> <Field type="ulong" name="maximumBucketSize" label="Maximum bucket 
> size" description="The maximum bucket length (entries in a single 
> bucket)" />
> <Field type="double" name="averageBucketSize" label="Average bucket 
> size" description="The average bucket length (entries in a bucket)" /> 
> <Field type="double" name="varianceOfBucketSize" label="Variance of 
> bucket sizes" description="How far bucket lengths are spread out from 
> their average value" />
> <Field type="double" name="stdDevOfBucketSize" label="Standard 
> deviation of bucket sizes" description="How far bucket lengths are 
> spread out from their mean (expected) value" />
> <Field type="double" name="addRate" label="Rate of addition" 
> description="How many items were added since last event (per second)" />
> <Field type="double" name="removeRate" label="Rate of removal" 
> description="How many items were removed since last event (per 
> second)" />
>
> This event was implemented for the following system tables:
>
> SymbolTable
> StringTable
> Placeholder Table
> LoaderConstraints Table
> ProtectionDomainCache Table
>
> Webrev:  http://cr.openjdk.java.net/~gziemski/8185525_rev1/
> Bug:     https://bugs.openjdk.java.net/browse/JDK-8185525
> Testing: Mach5 tier1,2,3 (another Mach5 tier1,2,3,4,5,6,7 in progress…)
>
>
> Cheers
>