Add client-side metrics to the ZooKeeper Java client#148
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Introduce ClientMetrics (mirroring ServerMetrics) and wire the existing pluggable MetricsProvider framework into the Java client. Client metrics are opt-in: the default provider is NullMetricsProvider, so there is no overhead unless explicitly enabled via the new zookeeper.clientMetricsProvider.className / .* client properties. ClientCnxn now emits, from a single request funnel and the SendThread lifecycle: - per-operation request latency and count - unsuccessful request counts labelled by KeeperException.Code - ping round-trip time and connect latency - connection established / loss / reconnect and session-expired counters The provider is a per-JVM singleton shared by all ZooKeeper instances so that, e.g., a Prometheus provider does not bind the same port twice. Adds unit and integration tests and a Client Metrics section to the monitor guide. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Description
Adds client-side metrics to the ZooKeeper Java client, built on the existing pluggable
MetricsProviderframework (which was always intended for client use, per ZOOKEEPER-3103). Until now only the server emitted metrics viaServerMetrics; the Java client emitted none.ClientMetricssingleton (mirroringServerMetrics) plus instrumentation inClientCnxn. It records per-operation request latency and count, unsuccessful-request counts labelled byKeeperException.Code, ping round-trip time, connect latency, and connection established/loss/reconnect and session-expired counters.queuePacket/finishPacket) and theSendThreadlifecycle. The feature is opt-in: the default provider isNullMetricsProvider(zero overhead), enabled via newzookeeper.clientMetricsProvider.className/zookeeper.clientMetricsProvider.*client properties onZKClientConfig. The provider is a per-JVM singleton shared by allZooKeeperinstances so a real provider is not booted twice (e.g. Prometheus port binding).Tests
The following tests are written for this issue:
ClientMetricsTest(unit — singleton, per-op latency/count, error-by-code, lifecycle counters/summaries)ZKClientConfigMetricsTest(unit — provider class-name default/override andmetricsProvider.*passthrough)ClientMetricsIntegrationTest(integration — real client↔server; asserts create/getData counts, NONODE error count, and connection-established are emitted)The following is the result of the "mvn test" command on the appropriate module (
zookeeper-server):Existing
ZKClientConfigTest(6) still passes. (Note: JMX-harness integration tests are broken in this local environment under Java 25/RMI, unrelated to this change; the metrics integration test is self-contained and avoids that harness.)Changes that Break Backward Compatibility (Optional)
None. The feature is purely additive and opt-in: with no configuration the client uses
NullMetricsProvider, so existing behavior and overhead are unchanged.Documentation (Optional)
Adds a "Client Metrics" section to
zookeeper-docs/.../zookeeperMonitor.mddocumenting how to enable the provider, the per-JVM semantics, and the emitted metrics.🤖 Generated with GitHub Copilot CLI