[yordis]

• When the advisory lock pool dies while Postgres refuses new connections, the lock server can wait forever on a request nothing will answer, so every subscription of the event store crashes on its lock call and none can subscribe again until the lock server or the event store restarts.
• While the lock pool is down for its restart backoff, lock calls block instead of failing, so subscriptions stall rather than retrying on their own schedule.

---

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PR Summary

Medium Risk
Changes failure modes and supervision wiring for subscription advisory locks; incorrect handling could still break lock acquisition or reconnect behavior under DB outages.

Overview
Fixes advisory lock requests hanging indefinitely when the dedicated lock Postgrex pool dies or is restarting (e.g. Postgres refusing connections), which previously blocked subscriptions until a full restart.

EventStore.AdvisoryLocks now takes a separate monitor (MonitoredServer) from the pool conn name. Lock acquire, unlock, and session checks run through query/2, which turns a pool :exit into {:error, DBConnection.ConnectionError} instead of leaving the GenServer stuck on a dead checkout.

EventStore.Supervisor registers the advisory-lock Postgrex pool under the conn name while the MonitoredServer keeps its own name/id; AdvisoryLocks is started with both.

New tests cover in-flight lock calls when the pool is killed, behavior while the pool is down (no long wait for restart backoff), and that suspending the monitor does not take down the lock server.

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• lib/event_store/advisory_locks.ex

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Walkthrough

The advisory-lock process now monitors a dedicated server. Lock acquisition, session verification, and release use the connection pool. Pool exits return connection errors. Tests cover pool failure behavior and monitor suspension.

Changes

Advisory-lock pool handling

Layer / File(s)	Summary
Configure the advisory-lock monitor lib/event_store/advisory_locks.ex, lib/event_store/supervisor.ex	The advisory-lock state now requires a monitor process. The supervisor configures a dedicated monitored-server name and passes it to AdvisoryLocks, which monitors that process.
Run advisory-lock operations through the pool lib/event_store/advisory_locks.ex, test/advisory_locks_test.exs	Lock acquisition, session verification, and release now use the pool. Pool exits become connection errors. Tests cover in-flight errors, immediate failure when the pool is unavailable, monitor suspension, and pool process handling.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~12 minutes

Change: Bug fix

Suggested reviewers: slashdotdash

Merge Risk: ⚪ Minimal · up to 20e5c

Lock calls now return errors when the pool is unavailable rather than waiting on its monitor. No actionable merge-blocking regression was established.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 18.18% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 11 functions across 4 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: preventing advisory-lock queries from waiting indefinitely when the lock pool stops.
Description check		The description directly explains the two failure scenarios that the changes address: indefinite lock-query waits and blocked subscription retries during lock-pool recovery.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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_{A rabbit checks the lock pool’s gate
Queries return errors, not a wait
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Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @lib/event_store/advisory_locks.ex:
- Around line 279-294: Move the `MonitoredServer.whereis/1` call inside the
`try`/`catch` in `with_pool/2` so exits from the lookup, as well as from
`query.(pool)`, are converted to `ConnectionError` results. Preserve the
existing handling when the lookup returns `nil`.

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📒 Files selected for processing: 3

• lib/event_store/advisory_locks.ex
• lib/event_store/monitored_server.ex
• test/advisory_locks_test.exs

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