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## Why Database pressure currently collapses several distinct delays into one symptom. This adds the evidence layer needed to distinguish pool acquisition wait, logical database operation time, advisory-lock wait, and selected transaction duration before changing timeout or retry policy. This is the phase 2 Lane A observability bundle for [#26](https://github.com/TheSentinel454/buzz/issues/26), [#28](https://github.com/TheSentinel454/buzz/issues/28), and [#33](https://github.com/TheSentinel454/buzz/issues/33). It is stacked on #6668. ## What - Record explicit reader/writer checkout wait and acquisition outcomes with `buzz_db_pool_acquire_wait_seconds` and `buzz_db_pool_acquisitions_total`. - Extend the compile-time `#[datastore_span(name = "...")]` seam with `buzz_db_operation_duration_seconds`, so operation labels remain static source literals instead of request data. - Route correctness-critical replacement, membership, push-gate, deletion, and migration/schema-safety advisory locks through one observer without changing their SQL, order, scope, or blocking behavior. - Measure six internally owned transaction lifetimes with `buzz_db_transaction_duration_seconds`, starting after `BEGIN` succeeds and ending after explicit commit/rollback or scope exit. - Emit root slow-operation warnings at 500 ms, logging the first slow completion and then 1/100 per call site with only `operation`, `outcome`, and `elapsed_ms`. - Document names, units, fixed label vocabularies, measurement boundaries, and blind spots in this PR description. Fixed labels are deliberately small: - `pool_role`: `writer`, `reader` - `lock_type`: `replacement`, `membership`, `push_gate`, `deletion`, `migration_schema_safety` - `outcome`: `success`, `error`, `timeout` where SQLx/PostgreSQL can distinguish it accurately - `operation`: compile-time datastore names plus the six closed transaction operation names documented in the runbook No metric or slow warning contains community IDs, event IDs, event kinds, coordinates, d-tags, SQL/query text, query IDs, returned errors, or event content. ## Coverage boundaries - Operation duration is the complete annotated logical function body, not pure SQL execution; it may include implicit checkout, lock wait, nested operations, and application work. Cancelled futures do not reach its completion hook. - Pool timing covers explicit helper checkouts, including proved-reader routing and selected writer-owned transactions. Implicit SQLx checkout through `&PgPool` remains folded into operation duration. - Lock timing covers application-side blocking locks in the five named families. Trigger/stored-procedure locks, channel-TTL locking, the usage try-lock, and the audit service session lock remain outside this slice. - Transaction timing covers only the six wholly owned boundaries documented in the runbook. It excludes pool wait, `BEGIN`, asynchronous rollback cleanup after an early return, and caller-owned `Db::begin_transaction` lifetime. ## Relationship to #6229 #6229 is the incident-driven timeout precursor. This PR does not add or change `statement_timeout`, `lock_timeout`, `idle_in_transaction_session_timeout`, retries, audit durability, or client-visible conflicts. It provides the missing distributions needed to evaluate those policies later and intentionally leaves #6229's open audit retry/durability finding untouched. The branches overlap in `crates/buzz-db/src/lib.rs` and `crates/buzz-db/src/migration.rs`, so a later rebase may need textual conflict resolution, but the behavior is complementary rather than duplicated. ## Risk assessment Moderate-low. The primary risk is instrumentation overhead and added static series. Cardinality is source-bounded, slow logs are sampled/redacted root events, and the lock/transaction changes wrap existing awaits without changing policy or ordering. ## Verification Author workstation: `buzz-tornquist-db-pressure-observability` (`2010927`), exact head `d7cf833e26c528adfcde3917ded80daf6f4ddac9`, parent `6f50e6b2b2a996349149af61d35bdd6a355f77fd`. - `cargo fmt --all --check` — passed - `cargo clippy -p buzz-datastore-tracing -p buzz-db -p buzz-audit -p buzz-search -p buzz-relay --all-targets -- -D warnings` — passed - `cargo test -p buzz-datastore-tracing --quiet` — 4 passed - `cargo test -p buzz-db --quiet` — 109 passed, 200 ignored - `cargo test -p buzz-audit -p buzz-search --quiet` — 16 passed, 25 ignored - `cargo test -p buzz-relay --lib --quiet -- --test-threads=1` — 906 passed, 48 ignored - Native PostgreSQL focused tests for pool success/timeout/error, lock success/contention/timeout/error, replacement, membership serialization, push ordering, deletion fencing, migration/schema exclusion, and reader fallback — 8 passed The default-parallel relay run passed once; subsequent runs exposed the existing load-sensitive `api::mesh_demo::tests::demo_join_forwarded_arm_round_trips_echo` 504 at the end of the suite. That test passes in isolation and the full relay suite passes serially. Independent exact-head review workstation: `buzz-tornquist-db-pressure-observability-review` (`2013067`). Formatting, the same all-target clippy command, datastore instrumentation tests, DB unit tests, source privacy guards, and diff/non-goal audits passed; no review findings. Generated with Codex --------- Signed-off-by: tornquist <tornquist@squareup.com>