[pcbeingused333]

Summary

MeteredManagedHttpClientConnectionFactory.createConnection adds the connection creation time to a ConcurrentLinkedQueue on every new pooled connection, but the queue is only drained by getTime(), which only the Micrometer gauge calls, and that gauge is registered only when a metrics registry is configured. Without a registry (the default, and always in jdbc-v2), one queue node is retained per new connection for the life of the Client.

The factory now records times only after enableMetrics() is called, which HttpAPIClientHelper does only when a metrics registry is present, right before the gauge is bound. Behaviour with a registry is unchanged.

Closes #3253

Checklist

• Closes [client-v2] Connect-time queue of the pooled connection factory grows without limit when no metrics registry is set #3253
• Unit and integration tests covering the common scenarios were added (MeteredConnectionFactoryTest: nothing is queued without metrics; times are recorded and drained once enabled. The first test fails before the fix with expected 0, found 10.)
• A human-readable description of the changes was provided to include in CHANGELOG (history/latest/3253.md)

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This PR was prepared with the assistance of an AI coding tool (Claude); the change was reviewed before submission.

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Note

Low Risk
Targeted leak fix behind a flag; metrics-enabled behaviour is unchanged and covered by new unit tests.

Overview
Fixes a memory leak in pooled HTTP clients when no metrics registry is configured (the default for client-v2 and jdbc-v2).

MeteredManagedHttpClientConnectionFactory previously appended every new connection’s creation duration to an internal queue, but that queue is drained only via getTime() when Micrometer binds the connect-time gauge. Without a registry, entries were never removed and grew with each new connection for the client’s lifetime.

The factory now gates timing behind enableMetrics(), which HttpAPIClientHelper calls only when a metrics registry is present. createConnection skips queueing when metrics are off; behaviour with Micrometer unchanged. Unit tests in MeteredConnectionFactoryTest cover both paths, and history/latest/3253.md documents the fix for #3253.

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Metrics stay enabled after bind failure

Medium Severity

enableMetrics() runs before the Micrometer binders and is not turned off when registration fails. The client then keeps enqueueing connection times with no gauge calling getTime(), so the unbounded times queue this change addresses can still grow for the lifetime of the Client.

Additional Locations (1)

• client-v2/src/main/java/com/clickhouse/client/api/internal/HttpAPIClientHelper.java#L1387-L1403

 

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