clickhouse-managed-postgres-rca

ClickHouse Managed Postgres RCA

When to use

Trigger whenever a user reports slowness, high CPU, low
throughput, cache thrash, or any unexplained pain on a
ClickHouse-managed Postgres instance.

What you have access to

Two APIs on https://api.clickhouse.cloud (HTTP Basic auth
using a ClickHouse Cloud API key/secret pair):

• Prometheus metrics — operation postgresInstancePrometheusGet
  under the Prometheus tag. Returns Prometheus exposition format.
  System and workload metrics for one Postgres service.
• Slow Query Patterns — operation slowQueryPatternsGetList
  under the Postgres tag. Returns per-digest latency, IO, and
  call statistics for normalized query patterns. Beta.

Both endpoints require an organizationId and a serviceId as
path parameters. The user must supply both, plus the API
key/secret pair.

What you do NOT have

• Query plans / EXPLAIN output.
• Per-table scan-type counters (seq_scan / idx_scan).
• Autovacuum or last-ANALYZE timestamps.

Reason from IO and timing signals, not from a plan tree.

Workflow

Six steps, in order. Do not skip ahead.

Steps 2 and 3 only share auth — no data dependency between
them. Run them in parallel (background curls, & + wait) to
cut wall time from sequential ~2s to ~1s.

1. Discover the live API shape

These endpoints are Beta — paths, params, and JSON field names
can shift. Follow rules/openapi-discovery.md to:

1. Fetch the OpenAPI spec from https://api.clickhouse.cloud/v1.
2. Locate the two operations by operationId:
   • postgresInstancePrometheusGet (Prometheus tag)
   • slowQueryPatternsGetList (Postgres tag)
3. Resolve their path templates, required query parameters,
   and (for the slow-query endpoint) the response schema.
4. Build a session-scoped role map from the schema property
   descriptions: { semantic role → actual field name }.

Use the resolved names in every subsequent request and citation.
Never hardcode field names from memory.

2. Scrape Prom once for system gauges

Follow rules/prometheus-scrape.md. One scrape, no wait.
You're after gauges (current values) that don't need a delta:
CacheHitRatio, ActiveConnections, MemoryUsedPercent,
FilesystemUsedPercent.

A CacheHitRatio well below ~95% on a workload that should
fit in cache is a real signal on its own. Climbing
ActiveConnections toward the pool ceiling is a real signal
on its own. These don't need rate-of-change.

A second scrape for counter deltas is opt-in, used only
when Step 4 triage points at write-congestion (where deadlock
and rollback rates matter and the Slow Query Patterns API
can't substitute). For the read-path case (the most common
RCA shape) the single scrape is enough.

3. Pull top slow query patterns

Request the slow query patterns. Follow
rules/slow-query-patterns-fields.md for the fields that
matter and how to read them. This is the primary diagnostic —
it returns per-pattern accumulated totals (call count, runtime,
blocks, rows) over the window you request, which is the
"rate-of-change" data you'd otherwise derive from two Prom
scrapes — but per query and without waiting.

If no patterns return a meaningful totalDurationUs, the
report may be overstated or the issue isn't query-shaped.
Stop and tell the user what you looked at.

4. Triage: pick the right heuristic

Follow rules/triage.md. Match the combined Prom + slow-query
signal to one of the heuristic shapes. Each shape points to a
specific heuristic file:

• rules/heuristic-full-scan.md — read-path full scan.
• rules/heuristic-hot-loop.md — N+1 / hot loop from the app.
• rules/heuristic-write-congestion.md — deadlocks, slow
  writes, high rollback rate.

If the signal does not match any shape cleanly, do not invent
a hypothesis. Surface the top patterns and ask the user which
workload they recognize. New heuristics are welcome as PRs.

5. Reason, then recommend

Use the format in rules/output-template.md. Always include:
symptom, evidence, hypothesis (noting any alternative cause
you cannot rule out from this surface alone), short-term fix,
and long-term follow-ups.

6. Do not apply the fix

Follow rules/recommend-only.md. Never run DDL. Never call
pg_cancel_backend or pg_terminate_backend. Write the
recommendation, explain why, and let the human apply it.

Full Compiled Document

For the complete guide with every rule expanded in a single
context load: AGENTS.md.