## What
Follow-up to #4539. The driver-adapter work is inert until a client
flips to the pg driver adapter, but the moment one does, our database
observability degrades: the OTel metrics pipeline reads pool stats from
Prisma's `$metrics`, which is owned by the Rust engine's `quaint` pool.
Under the adapter, `pg.Pool` owns the pool, so those gauges read zero.
The pipeline also only ever scraped a single client (the control-plane
writer singleton).
This PR makes database metrics driver-agnostic and per-client:
- Every configured client registers a metrics source: control-plane
writer/replica, run-ops writer/replica, legacy writer/replica.
Previously only the control-plane writer singleton was scraped.
- Each OTel instrument is observed per client with `db_client` and
`db_driver` (`quaint` | `pg-adapter`) attributes. `db_client` uses our
canonical datasource-role labels (`control-plane-writer`,
`control-plane-replica`, `run-ops-writer`, `run-ops-replica`,
`legacy-run-ops-writer`, `legacy-run-ops-replica`) — the same strings
used for the `db.datasource` span attribute, so a metric and a trace
point at the same pool.
- Pool figures come from the authoritative source per driver:
- **pg-adapter**: `pg.Pool` (`totalCount`/`idleCount`/`waitingCount`,
plus cumulative opened/closed from `connect`/`remove` events).
- **quaint**: the Rust engine's `$metrics` pool gauges/counters, exactly
as before.
- Query counters and duration histograms still come from `$metrics` for
both drivers (the Rust engine executes queries in both cases).
- New `db.pool.connections.waiting` gauge (pg.Pool exposes this; quaint
reports 0).
- Stops exporting Prisma metrics from the Prometheus `/metrics` route.
Pool observability now lives entirely in the OTel pipeline, per driver,
per client.
## Why
So we can flip any client (including the control-plane writer, the
primary desync-fix target) to the driver adapter without losing pool
visibility. Existing dashboards keyed on the same metric names keep
working; they gain a per-client dimension.
## Testing
Unit (`apps/webapp/app/utils/databaseMetrics.server.test.ts`): the pure
normalizer — quaint reads pool from `$metrics`; adapter reads pool from
`pg.Pool` and keeps engine query metrics; `busy` never goes negative;
graceful zeroing when `$metrics` is unavailable (adapter still reports
live pool figures).
Live smoke test against a prod-shaped local stack: three
physically-distinct Postgres DBs (control-plane, run-ops, legacy) behind
dual PgBouncers, split mode on, with a mix of adapter and quaint
clients. Reading the actual emitted OTel metrics, every pool shows up as
its own series:
```
db.pool.connections.total{db_client="control-plane-writer", db_driver="pg-adapter"} = 1
db.pool.connections.total{db_client="control-plane-replica", db_driver="quaint"} = 1
db.pool.connections.total{db_client="run-ops-writer", db_driver="pg-adapter"} = 1
db.pool.connections.total{db_client="run-ops-replica", db_driver="quaint"} = 1
db.pool.connections.total{db_client="legacy-run-ops-writer", db_driver="quaint"} = 1
db.pool.connections.total{db_client="legacy-run-ops-replica",db_driver="quaint"} = 1
db.client.queries.total{db_client="control-plane-writer",db_driver="pg-adapter"} = incrementing
db.client.queries.duration.count{db_client="control-plane-writer",db_driver="pg-adapter"} = incrementing
```
Confirms: metrics are attributed per pool with the correct driver;
adapter pools' figures come from `pg.Pool`; and query counters/duration
histograms keep incrementing under the pg adapter. Also verified
`/metrics` (Prometheus) now returns zero `prisma_*` series while still
serving the app's own metrics.
`pnpm run typecheck --filter webapp` passes.
## Notes
- `/metrics` (Prometheus) no longer includes `prisma_*` series. Anything
scraping that endpoint for Prisma metrics should read the equivalent
`db.*` metrics from the OTel exporter instead.
- **PgBouncer + `?schema=` gotcha (separate from this PR, worth flagging
for rollout):** since #4539 parses `?schema=` from the DSN and passes `{
schema }` to the adapter, node-postgres sends `search_path` as a startup
parameter. A transaction-mode PgBouncer rejects that with `FATAL:
unsupported startup parameter: search_path`. Our prod control-plane DSNs
use the default `public` schema with no `?schema=` param, so this is
latent, but any client we flip to the adapter must not carry `?schema=`
in its DSN (or the pooler needs `ignore_startup_parameters =
search_path`).
---------
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Eric Allam
951d8e8d7b