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## Why A wedged relay boot pod holding a relation lock can park every other writer in the fleet behind it: DB load pins at pool capacity in `Lock:relation` waits while CPU stays flat, and nothing server-side releases the lock until the holder dies. We hit exactly this in production — ~1,400 sessions queued behind one crash-looping pod's boot transaction for ~20 minutes until kubelet killed the container. ## What Applies session-level Postgres timeouts to every **writer** connection inside the existing single `after_connect` hook in `buzz-db`, all env-tunable through the same `Config::from_env → DbConfig` path as the existing pool-size knobs: | Env var | GUC | Default | Effect | |---|---|---|---| | `BUZZ_DB_LOCK_TIMEOUT_MS` | `lock_timeout` | 5000 | statements waiting on any lock fail fast instead of parking behind a wedged holder | | `BUZZ_DB_IDLE_TXN_TIMEOUT_MS` | `idle_in_transaction_session_timeout` | 60000 | reaps wedged clients idling inside an open transaction while holding locks | | `BUZZ_DB_STATEMENT_TIMEOUT_MS` | `statement_timeout` | 0 (off) | opt-in runaway-statement cap; off by default because startup migrations/backfills legitimately run long statements | `0` disables a timeout (Postgres semantics) and deliberately passes through the env parsing — unlike the pool-size knobs where `0` falls back to the default. The reader pool is untouched: replica sessions never take contended locks and already fail acquire in 150 ms. Deployers tune these via plain env vars (`.env`, or `relay.extraEnv` in the Helm chart) — no code changes needed. ## Behavior change to note With the 5 s default `lock_timeout`, a boot-time migration or backfill that waits >5 s on a lock now errors (surfacing in logs / crash-looping the pod) instead of stalling silently. That is the intended visible-failure-over-fleet-stall tradeoff; deployers with slow contended migrations can set `BUZZ_DB_LOCK_TIMEOUT_MS=0`. ## Testing - `cargo test -p buzz-db -p buzz-relay` — buzz-db green; buzz-relay has 9 failures that also fail on clean `main` in this environment (api::admin/api::media/mesh_demo — unrelated, pre-existing). - New config test covers override / `0`-passthrough / invalid-fallback for all three env vars. - Extended the existing `writer_pool_safety_hook_is_single_and_composed` source-shape test so the timeouts can't drift out of the single `after_connect` hook (SQLx replaces hooks — a second hook would silently disarm the floor guard). - `cargo fmt --check` and `cargo clippy --all-targets` clean for the touched crates. Closest existing PR/issue: none found. --- **Update Aug 28, 17:06 EDT:** Rebased onto `main` at `a3730784fc` and addressed the latest correctness review. - Ported the timeout policy onto the refactored `buzz-db::runtime` pool constructor and kept the shared env overlay for relay, admin, deletion, and audit writers. - Migration/schema-destruction connections now disable `lock_timeout` and `statement_timeout` for their intentional long wait/DDL path. This supersedes the earlier “Behavior change to note”: contended boot migrations wait for the current migration owner rather than crash-looping after five seconds. - The audit worker now preserves and retries the same entry on PostgreSQL `55P03` lock timeouts, using exponential backoff capped at one second. Other database errors retain the existing terminal error behavior, and retries emit `buzz_audit_log_lock_retries_total`. - Added CI-backed PostgreSQL regressions for writer GUC installation/migration exemption, audit-pool lock timeouts, and worker recovery. The worker regression holds the real audit advisory lock past `lock_timeout`, observes a retry, releases the lock, and proves the original entry is appended exactly once. Current verification supersedes the earlier testing notes: workspace Rust clippy passed with warnings denied; all nine infrastructure-free backend unit-test lanes passed; all three focused PostgreSQL regressions passed against PostgreSQL 17; formatting, diff checks, file-size guards, and desktop frontend checks passed. The Linux Blox workstation could not run the unrelated Tauri native lane because `glib-2.0` is absent, so that platform check is left to PR CI. --- **Update Aug 31, 11:09 EDT:** Rebased onto current `main` at `c3132c3ee9` and reran the requested audit-lock contention scenario on Blox at head `896c3fe9ed`. - `git range-diff` reports both PR commits unchanged by the rebase; the branch remains two commits and the worktree is clean. - `cargo fmt --all -- --check` and clippy with warnings denied passed for `buzz-db`, `buzz-relay`, `buzz-admin`, and `buzz-deletion`. - All three focused PostgreSQL 17 regressions passed: writer session timeout/migration exemption, audit writer timeout bounds, and audit worker recovery of the original entry exactly once. - Live protocol verification used a head-built relay and CLI, native PostgreSQL 17/Redis, `BUZZ_DB_LOCK_TIMEOUT_MS=300`, and an eight-second hold on the community audit advisory lock. The real message was accepted and persisted once while the lock was held; its audit-row count remained zero during contention while retries accumulated. After release, exactly one `event_created` audit row appeared and remained exactly one after an additional two-second duplicate check. The run recorded nine lock-timeout retries, zero audit failures, and event ID `7f8c4ffae28e78555fcf2d56396d6e6c01b3712e5411288dc79e9a54af9d9444`. Generated with Codex --------- Signed-off-by: Luke Tornquist <tornquist@squareup.com>