ZOOKEEPER-4818 Add metric JVM_HEAP_BYTES_USED, JVM_HEAP_BYTES_MAX, and JVM_HEAP_BYTES_FREE

[joseph-bennett-sf]

https://issues.apache.org/jira/browse/ZOOKEEPER-4818

[maoling]

We already had this feature?

1. enable the metricsProvider.exportJvmInfo

cat conf/zoo.cfg
## Metrics Providers
#
# https://prometheus.io Metrics Exporter
metricsProvider.className=org.apache.zookeeper.metrics.prometheus.PrometheusMetricsProvider
metricsProvider.httpHost=0.0.0.0
metricsProvider.httpPort=7000
metricsProvider.exportJvmInfo=true

2. curl http://localhost:7000/metrics |grep "jvm_memory_bytes_"

[joseph-bennett-sf]

We already had this feature?

Is this only for the prometheus metrics provider? This information should ideally be available for implementations using other methods for exporting metrics. Please see ZOOKEEPER-4818

[maoling]

when applying this patch and enables the prometheus, the server cannot start up.

2024-06-19 17:24:51,895 [myid:] - ERROR [main:o.a.z.s.ZooKeeperServerMain@70] - Invalid arguments, exiting abnormally
java.lang.IllegalArgumentException: Collector already registered that provides name: jvm_memory_bytes_used
	at io.prometheus.client.CollectorRegistry.register(CollectorRegistry.java:54)
	at io.prometheus.client.SimpleCollector$Builder.register(SimpleCollector.java:246)
	at org.apache.zookeeper.metrics.prometheus.PrometheusMetricsProvider$PrometheusSummary.<init>(PrometheusMetricsProvider.java:499)

metricsProvider.className=org.apache.zookeeper.metrics.prometheus.PrometheusMetricsProvider
metricsProvider.httpHost=0.0.0.0
metricsProvider.httpPort=7000

[joseph-bennett-sf]

@maoling Thanks for the review. I believe this is due to the metric names conflicting with those that Prometheus exports. I have updated the names so that they do not conflict with each other.