## What
Exports three sets of metrics to Prometheus to diagnose the recurring
"Slow DB Query" Sentry issues on `POST /graphql` (e.g. the
`fieldMetadata` select):
- `twenty_nodejs_eventloop_delay_seconds` (mean/p50/p99/max) +
`twenty_nodejs_eventloop_utilization`
- `twenty_workspace_cache_recompute_duration_seconds{cache_key}` — wall
time per provider `computeForCache`
- `twenty_workspace_cache_redis_write_duration_seconds` — serialize +
Redis write time for recomputed entries
## Why
Investigation of these issues showed:
- The flagged query executes in ~1ms (prod EXPLAIN), so it is not a
query/index problem.
- Event counts do **not** correlate with connection-pool acquire latency
(Pearson ~0 against both p99 and the direct count of >1s acquires), so
it is not pool contention.
- Event counts **do** correlate with pod CPU (Pearson +0.40).
The leading explanation is that the slow `db` span is inflated by
event-loop saturation during the workspace metadata cache recompute:
`Promise.all` parallelizes the I/O, but the synchronous work it cannot
parallelize (TypeORM entity hydration of JSONB-heavy result sets, then
`JSON.stringify` of the flat-map payloads into Redis) blocks the single
event-loop thread, so an awaiting query resolves ~1.3s late.
Node event-loop delay was only being collected by Sentry's
`nodeRuntimeMetricsIntegration`, never exported to Prometheus, so it
could not be graphed or correlated in Grafana. These metrics confirm (or
refute) the mechanism and give a before/after baseline for the fix.
Grafana panels land in a companion twenty-infra PR.
## Notes
- Metric-only change; no behavioral change to the cache.
- Uses the same OTel `MetricsService` / meter as the existing DB pool
metrics.
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Charles Bochet
1ebcbdda42
