6d07a29137
## Why
The usage poller pays memory and query costs proportional to community
count even when per-community emission is disabled. Every pod loads the
full host map, and the leader materializes all per-community aggregates
before suppressing their labels. That makes telemetry collection itself
a scaling constraint.
## What changed
- Fleet-only usage metrics are now the default. `all` remains available
as an explicit rollback mode.
- In fleet-only mode, the poller skips the community host map and all
community-sized query results.
- Exact community counting is replaced with the PostgreSQL planner's
table-size estimate.
- Stock totals are collected as one fixed row, scanning each stock table
once per hour.
- 1d/7d/30d active-user totals come from one bounded 30-day scan per
day.
- Fleet database snapshots run only on a proved read replica, with a
telemetry-specific freshness budget and server-side statement timeouts.
If no such replica is available, the collection is skipped; it never
falls back to the writer.
- Successful fixed-row snapshots are cached and re-emitted on each poll
tick, so gauges stay scrape-visible without raising query frequency.
- `buzz_usage_snapshot_available{family}` reports whether the latest due
refresh of that family succeeded. After a skipped or failed refresh, the
last values stay visible (with `buzz_usage_snapshot_age_seconds`) but
the family reads unavailable until a 60-second retry succeeds.
- The `all` rollback collector publishes the same availability gauges,
so dashboards gated on availability keep working during a rollback.
- Each due refresh outcome is applied by `apply_stock_refresh` /
`apply_activity_refresh`, the single production mapping from `Ok(Some)`
/ `Ok(None)` / `Err` to cache, availability, skip counter, and retry;
the regression test drives that mapping directly.
- `buzz_usage_snapshot_age_seconds` is emitted in the `all` rollback
too, so age-based alerts keep firing through a rollback.
- Every fleet telemetry attempt that completes lands in
`buzz_db_route_decision`; a query error on a proved reader records
`skipped/replica_error`. An attempt abandoned at the relay deadline
records no route decision and appears only as
`buzz_usage_query_skipped_total{reason="timeout"}`. The shared
`proved_reader` warnings no longer claim "routing to writer", because
the telemetry caller never does (serving callers still record their
writer decision in the route counter).
- The PostgreSQL production-method matrix now exercises
`usage_fleet_stock_snapshot`, so the new `reader/maintenance` pool pair
is proven to be emitted by a real Db method.
- Each fleet collection, reader proof included, runs under a relay-side
`tokio::time::timeout` (10s stock, 20s activity, both above their
server-side `statement_timeout`). A reader that stops answering expires
into the same failure mapping with
`buzz_usage_query_skipped_total{reason="timeout"}`, so it cannot stall
the leader's poller, hold the advisory lock past a liveness check, or
leave a frozen snapshot reporting available.
- Fleet telemetry reader checkouts (`ReaderOperation::Maintenance`) opt
into SQLx `close_on_drop` before their first post-acquire await, so an
abandoned collection's connection is closed within SQLx's 5s
`CLOSE_ON_DROP_TIMEOUT` instead of going through the unbounded
return-to-pool ping while it holds a slot in the reader pool that
serving reads share. Serving reads keep pooled reuse; the cost is one
reader reconnect per fleet refresh.
- On leader demotion, cached snapshots and availability are cleared, and
a fresh collection is forced after the lock is reacquired.
- Fleet-only mode passes no host map to the worker-snapshot storage
emitter. It therefore omits community attribution instead of reporting
every byte as `buzz_storage_unmapped_community_bytes`.
- Lifetime stored-message and active-channel totals are no longer
queried in fleet-only mode. Event throughput remains available through
the existing stored-event counter.
- No test-selector changes: main's `config::tests::` selector in `just
test-unit` and the `run-tests.sh unit` fallback already runs the new
replica-budget config test, and the new fleet schedule, availability,
and storage tests run through the existing bin `tests::` and
`storage_sweep::tests::` selectors.
- Added seeded PostgreSQL contract tests and operator docs covering
rollout, rollback, availability, the no-replica behavior, and leader
election.
No migrations, tables, indexes, or new persistent storage are added.
### What got simpler
The relay-side storage half of the original branch (totals-only S3
listing and `buzz_storage_community_breakdown_available`) was dropped.
Main moved S3 listing out of the relay in #7543 and #7845, so that code
was dead on arrival. The rework adds no storage code path; it only gates
attribution on the presence of a host map.
## Risk
Medium. The default changes which telemetry is emitted:
- In fleet-only mode, `buzz_communities_estimated` replaces the exact
`buzz_communities_total`.
- `buzz_total_messages` and `buzz_total_active_channels` are not
refreshed in fleet-only mode (also called out in the rollout steps of
`docs/usage-metrics.md`).
- Deployments without a verified reader (including local compose and
single-node self-hosts) skip database-derived fleet snapshots instead of
querying the writer, and report both families unavailable.
- Multi-pod dashboards must filter database and storage series to
`buzz_usage_poller_is_leader == 1`.
Setting `BUZZ_USAGE_METRICS_PER_COMMUNITY=all` restores the legacy
collector for temporary rollback.
## Verification
At head `1879ee3aedf4227942120a3b521c8d35fc7839fe` (tree `78477e74`;
merges main `da651ad6`; the PR's diff against main is byte-identical to
`1613823f`'s, minus the Justfile and `run-tests.sh` selector lines that
main's `config::tests::` selector now subsumes):
- On Blox: `cargo fmt --all -- --check` and `cargo clippy -p buzz-db -p
buzz-relay --all-targets -- -D warnings` pass. Relay bin `tests::`
34/34, `config::tests::` 55/55, `storage_sweep::tests::` 10/10 and
`store::usage::tests` pass, as do the four `fleet_` and lock PostgreSQL
tests that use scratch databases, including
`abandoned_fleet_collection_releases_its_reader_slot`.
- Against a freshly migrated PostgreSQL database:
`store::usage::postgres_tests::` 14/14,
`storage_sweep::postgres_tests::` and `buzz-db --test
observability_source` 14/14 pass. The new reader code passes main's
crate-wide typed-acquisition and serving-table policy checks.
- E2E at `1613823f` is reused for this head. It ran in an isolated relay
against a real PostgreSQL primary and streaming standby. In 2/2 runs a
stock read went dark mid-result; the deadline abandoned it at about 10s,
the reader pool's active and size counts dropped to zero about 1s later,
and a fresh activity read and the scheduled stock retry succeeded on new
backends while the dark session stayed open. The `all`-mode and
healthy-replica controls also passed. Main's merged changes are on the
writer path and in startup step timing, and touch none of the reader
checkout, the `close_on_drop` seam, the fleet poller or the deadlines.
At head `1613823fa8ef1a423bc1a499c57bc40d692fcd4f` (tree `12bc6d1b`;
test/docs-only on top of `57749418`), on a Blox workstation:
- `cargo fmt --all -- --check` and `cargo clippy -p buzz-db -p
buzz-relay --all-targets -- -D warnings` pass. Relay bin `tests::` 34/34
pass.
- New PostgreSQL test
`abandoned_fleet_collection_releases_its_reader_slot`: a one-slot reader
pool behind a loopback proxy that goes dark mid-session; the collection
is cut at a deadline, then a later acquire must succeed in under 8s on a
fresh connection. The dark call runs on a fresh `Db` with a cold Aurora
capability cache, so the first post-acquire await is the capability
probe. It passes in 3.4s. With `close_on_drop` removed, or moved below
the probe await, it fails with `PoolTimedOut` after the 15s acquire
timeout. The other three `fleet_` PostgreSQL tests that use scratch
databases pass.
- `each_fleet_family_is_abandoned_at_its_own_deadline` now has an outer
timeout: replacing the stock deadline with a bare `.await` fails it
(`Elapsed`) instead of hanging.
At head `fd194ec79d6c6796d6764564de225ad56485cfc7` (tree `79e94727`,
main merged at `932228936`), on a Blox workstation:
- `cargo fmt --all -- --check` and `cargo clippy -p buzz-relay -p
buzz-db --all-targets -- -D warnings` pass.
- Relay bin `tests::` nextest selection: 27/27 pass (plus
`store::usage::tests`), including
`fleet_refresh_outcomes_drive_availability_through_production_mapping`
and the new `stalled_fleet_collection_times_out_into_failed_refresh`
(paused time: two never-completing collections are abandoned at exactly
10s + 20s; both families read unavailable with cached values kept,
`reason="timeout"` skips, retry scheduled; the next tick runs and
recovers; no route decision is recorded for an abandoned attempt) and
`each_fleet_family_is_abandoned_at_its_own_deadline`. Compile-time
asserts keep each deadline above its `statement_timeout`.
- Falsifiability: replacing the stock deadline with a bare `.await`
makes the new test fail (the tick stalls); swapping the two deadlines
fails the per-family test; deleting `schedule.mark_stock_failure(now)`
from the `Ok(None)` arm fails the mapping test. Trees restored and
re-verified.
- At `970414db`: CI PostgreSQL Tests 809/809 including the
production-method matrix with `reader/maintenance`; Unit Tests ran
`finish_usage_read_records_every_attempt_in_route_decisions`.
- `just ci` / `just test` at `5b18914a` on Blox: not green for
environmental reasons (`mobile-check` could not reach pub.dev;
`_ensure-services` failed so service-backed suites did not run;
`buzz-acp git_bootstrap` fails identically on `origin/main`). PostgreSQL
and integration coverage comes from GitHub CI at this head.
E2E at the previous head `0a01e5f22` (isolated relay, real Postgres
primary plus streaming replica, worker storage snapshot, desktop
frontend in relay mode): with no reader, both families report
skipped/unavailable and route `skipped/disabled` (no writer queries);
fleet-only storage emits totals without `buzz_community_storage_*` or
unmapped bytes; `all` mode reports both availability gauges `1` with
per-community storage series; with a fresh replica, both fleet paths
route `replica/fresh` on `reader/maintenance` acquisitions; desktop
send/receive works. The cached success → due failure → recovery
transition was not reached live (hourly/daily cadence); it is covered by
the seam test above.
The original branch also recorded live verification at `aa3e7023`,
before this rework: reduced-idle cache re-emission, two-relay leader
takeover with demoted availability clearing, the no-reader skip with
60-second retry, `all` rollback restoring per-community series, and a
desktop smoke test. Those runs predate the availability and storage
changes and are not claimed for this head.
## Linear tracking
Related work: BUZZ-167.
---------
Signed-off-by: tornquist <tornquist@squareup.com>
Signed-off-by: Luke Tornquist <tornquist@squareup.com>
Signed-off-by: Elrond <28d6302a099e5225b02c4155ac4236e4912603df2ab08dbfc2f4fef08ce598c8@buzz.block.builderlab.xyz>
Co-authored-by: Elrond <28d6302a099e5225b02c4155ac4236e4912603df2ab08dbfc2f4fef08ce598c8@buzz.block.builderlab.xyz>
5.1 KiB
Usage metrics operations
The relay emits fleet-wide usage and storage gauges without retaining one in-memory series per community. This is the default, bounded-cardinality mode:
BUZZ_USAGE_METRICS_PER_COMMUNITY=off
BUZZ_USAGE_METRICS_REPLICA_MAX_AGE_MS=30000
Database-backed fleet gauges are replica-only. The replica freshness budget is
independent of BUZZ_REPLICA_READ_MAX_AGE_MS, which controls serving reads. A
missing, stale, or unavailable reader skips the telemetry query; the relay never
falls back to the writer for these aggregates. Set the telemetry budget to 0
to disable the database-backed families explicitly.
A deployment with no READ_DATABASE_URL, or whose reader fails verification,
therefore emits none of the database-backed fleet totals (buzz_total_users,
buzz_total_channels, buzz_total_active_users, and the rest of the stock
family) and reports both families unavailable. That includes local compose and
single-node self-hosts. Configure a verified reader where those totals are
needed.
Availability
Dashboards and monitors must pair values with these fixed-cardinality gauges:
buzz_usage_snapshot_available{family="stock"}buzz_usage_snapshot_available{family="activity"}
Database and storage gauges are leader-only. In a multi-pod deployment, first
filter them to the pod where buzz_usage_poller_is_leader == 1; do not take an
unfiltered maximum across pods. A demoted pod clears its snapshot availability,
but previously exported value series remain scrape-visible until the recorder
evicts them.
Availability reports whether the latest due collection of that family
succeeded. A value of 0 means it was skipped or failed; it must not be
interpreted as all usage being zero. The last successful values stay
scrape-visible while availability is 0, and
buzz_usage_snapshot_age_seconds{family=...} reports how old they are. Failed
stock or activity collections retry after 60 seconds; a successful retry
restores availability and resumes the normal hourly and daily cadences.
Each skipped or failed collection increments
buzz_usage_query_skipped_total{family,reason}: reader_unavailable when no
fresh proved reader was available, query_error when the reader query failed,
and timeout when the whole collection (reader proof included) exceeded its
relay-side deadline of 10 seconds for stock or 20 seconds for activity. The
deadline bounds a reader that stops answering, which the server-side statement
timeout cannot, so a hung reader cannot stall the leader's poller. Telemetry
reader connections are closed when the collection ends rather than returned to
the reader pool, and an abandoned one is closed within 5 seconds, so an
abandoned telemetry read cannot hold a slot that serving reads need.
Storage totals come from the buzz-admin worker snapshot and carry their own
buzz_storage_snapshot_load_ok and buzz_storage_snapshot_age_seconds health
gauges. In fleet-only mode the relay does not attribute storage to communities,
so it emits neither buzz_community_storage_* series nor
buzz_storage_unmapped_community_bytes.
Every fleet telemetry query attempt that completes is recorded in
buzz_db_route_decision{path=~"usage_fleet_.*"}: replica/fresh when it ran on
a proved reader, skipped/<reason> when no fresh proved reader was available,
and skipped/replica_error when the reader query itself failed. A collection
the relay abandons at its deadline records no route decision; it appears only
as buzz_usage_query_skipped_total{reason="timeout"}. None of these paths fall
back to the writer.
Rollout and rollback
- Deploy with per-community mode unset or
offand the telemetry replica freshness budget at its 30000ms default. - Update dashboards to use fleet gauges and gate alerts on the availability gauges above.
- Remove dependencies on the retired per-community series before increasing community count.
buzz_total_messages and buzz_total_active_channels are emitted only by the
all collection. In the default fleet-only mode they stop updating, so move
dashboards off them before rollout.
BUZZ_USAGE_METRICS_PER_COMMUNITY=all temporarily restores the prior
per-community emission for rollback or dashboard migration. It also restores
the associated memory and monitoring-cardinality growth, so it is not the
steady-state configuration. In this mode every leader tick collects all
families, so a successful collection reports both availability gauges as 1
and a failed one demotes the leader and reports 0; dashboards gated on
availability or buzz_usage_snapshot_age_seconds keep working through a
rollback. It emits the exact
buzz_communities_total instead of buzz_communities_estimated.
Leader election
Every relay process attempts the same PostgreSQL session advisory lock. Exactly one live database session owns it and performs collection. If that process or session exits, PostgreSQL releases the lock and another relay acquires it. The lock only deduplicates collectors; it does not permit writer fallback for fleet queries. A process that loses the lock clears its cached fleet snapshots, marks their availability as zero, and forces fresh collection if it later becomes the leader again.