pool: release stopped host reconnection handlers - #1032
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Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review. 📝 WalkthroughWalkthroughStopped reconnection handlers now release the host's reconnection slot after authentication failure, retry exhaustion, or an empty retry schedule. Cluster down-event handling tracks pending work and generations while coordinating reconnection restarts and host-addition state. Unit tests cover handler termination and down-event processing. Sequence Diagram(s)sequenceDiagram
participant Cluster
participant Host
participant Executor
participant ReconnectionHandler
Cluster->>Host: check down-event state
Cluster->>Executor: submit eligible restart
Executor->>Cluster: run restart after state checks
Cluster->>ReconnectionHandler: start handler
ReconnectionHandler->>Host: release slot when retries stop
Suggested reviewers: Priority: ➖ Normal Change: Bug fix · Severity of issue fixed: Medium Merge Risk: ⚪ Minimal · up to Hosts whose reconnection attempts stopped after authentication failure or retry exhaustion can now start a fresh reconnection on a later DOWN event. DOWN and UP handling was also serialized, and no defect was found that would leave a host stuck without reconnection. The change appears ready to merge. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
✨ Finishing Touches 💡 1⚔️ Resolve merge conflicts 💡
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Actionable comments posted: 1
- 🪄 Fix CodeRabbit comments on this PR
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Inline comments:
In `@cassandra/cluster.py`:
- Around line 2185-2193: Update the refresh path to use a new
Cluster.remove_host_by_host_id wrapper with refresh_nodes disabled instead of
calling Metadata.remove_host_by_host_id directly. Implement the wrapper so it
invokes on_remove only when the host was actually removed, not when the same
Host was reindexed under another ID, preserving cleanup of profiles, pools,
listeners, and reconnection state.
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cassandra/cluster.pycassandra/pool.pytests/unit/test_cluster.py
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Authentication failures and exhausted retry schedules left their handlers installed, so every later DOWN event treated a stopped handler as active and permanently skipped the host. Release terminal handlers without clearing a concurrent replacement, let later DOWN events start a fresh retry cycle, and serialize pending lifecycle transitions so stale restart work cannot replace newer recovery state. Fixes #1026
Clear the pending host addition atomically with marking the host up, so listener callbacks observe a completed lifecycle. This prevents concurrent DOWN handling from starting an add-mode reconnector and ensures listener exceptions cannot leave the flag stuck.\n\nCover both cases by sending DOWN and raising from an on_add listener.
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Problem
_HostReconnectionHandlerstayed installed inhost._reconnection_handlerafter an authentication failure or after exhausting its retry schedule.Cluster.on_down()then treated that stopped handler as an active reconnection and skipped every later attempt, permanently losing the host for the lifetime of the cluster.Fix
Release the host reconnection slot whenever its handler will not run again. Clear the slot under the host lock only when it still points to that handler, so a concurrent replacement remains installed.
Allow a later DOWN event for the already-down host to start a fresh retry cycle without repeating the original DOWN notifications. Serialize pending DOWN and restart work, preserve pending host-addition semantics, and discard stale restart work after a newer DOWN or UP transition.
No public API, wire protocol, or compatibility behavior changes. The change is limited to host reconnection and the lifecycle state needed to restart it safely.
Fixes #1026
Deferred follow-ups
Neither follow-up is introduced by this PR or a release blocker for #1026.
Testing
TZ=UTC uv run pytest -q tests/unit— 1071 passed, 40 skippedTZ=UTC uv run pytest -q tests/unit/test_cluster.py— 73 passedgit diff --checkPre-review checklist
./docs/source/. (Not applicable: internal behavior fix; changelog updated.)Fixes:annotations to PR description.