adding-ingestion-warnings

Development

How to add a new ingestion warning type to the event ingestion pipeline. Use when emitting a new warning from nodejs ingestion code (emitIngestionWarning, captureIngestionWarning, pipeline `warnings` arrays, `drop()` with warnings), when adding a warning type, category, or severity, or when a typecheck error says a string is not assignable to IngestionWarningType. Covers the INGESTION_WARNING_TYPES registry (the single source of truth for type, category, and severity), the details-key conventions that ClickHouse v2 materializes into columns, debouncing, and the downstream surfaces to keep in sync (v1 UI map, docs, v2 API).

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Adding ingestion warnings

Ingestion warnings tell customers their events were ingested with problems (or dropped). They are produced to the clickhouse_ingestion_warnings Kafka topic and land in two ClickHouse tables: v1 (ingestion_warnings) and v2 (ingestion_warnings_v2, which materializes structured columns from the details JSON).

The registry is the source of truth

Every warning type must be registered in INGESTION_WARNING_TYPES in nodejs/src/ingestion/common/ingestion-warnings.ts. The registry fixes the type's category and severity; they are resolved at serialization time, so callsites cannot drift or forget them. An unregistered type is a compile error (IngestionWarningType is the registry's key union).

To add a new warning:

Register the type in INGESTION_WARNING_TYPES, inside the matching group comment block. Pick:
- category — one of size, merge, event, transformation, replay. Extend IngestionWarningCategory only when the warning genuinely doesn't fit an existing group; new categories flow into API filters and agent-facing docs, so keep the vocabulary small.
- severity — follow the convention: error = the event or message was dropped, warning = ingested but modified or partially rejected, info = informational or an intentional, team-configured drop.
Emit it (see below), passing only per-occurrence fields: details, pipelineStep, optional key / alwaysSend.
Update downstream surfaces (see checklist).

Emitting

Two paths, both end at serializeIngestionWarning:

Pipeline steps (preferred): return warnings on the result — ok(value, sideEffects, warnings) or drop(reason, [], warnings). They accumulate in context.warnings and are sent by handleIngestionWarnings(), which requires a teamAware() block. See the framework doc test 09-ingestion-warnings.
Direct emit: emitIngestionWarning(outputs, teamId, warning) (outputs-based, preferred) or captureIngestionWarning(kafkaProducer, teamId, warning) (legacy) for code outside the pipeline result flow.

Details keys ClickHouse v2 materializes

ingestion_warnings_v2 derives columns from these exact JSON key names (see posthog/models/ingestion_warnings/sql_v2.py) — use them, don't invent variants:

details key	v2 column
`eventUuid`	`event_uuid`
`distinctId`	`distinct_id`
`personId`	`person_id`
`groupKey`	`group_key`

category, severity, and pipelineStep are appended to details by the serializer — never set them in details yourself; a stray key cannot override them (structured fields are spread last).

Debouncing

Warnings are rate-limited per team:type:key. Set key to the entity you want to debounce by (e.g. a distinct ID) and alwaysSend: true only for warnings that must never be dropped by the limiter.

Rust

No Rust service emits ingestion warnings today — the Rust capture service only routes $client_ingestion_warning events to Kafka; the nodejs pipeline turns them into warnings. If a Rust service ever needs to produce to clickhouse_ingestion_warnings directly, mirror the nodejs registry in a Rust module (type enum with category() / severity()), keep the JSON shape identical to serializeIngestionWarning, and update this skill to point at it.

Downstream checklist

When adding a type, also update:

v1 UI map — WARNING_TYPE_TO_DESCRIPTION (and WARNING_TYPE_TO_DOCS_ANCHOR if documented) in frontend/src/scenes/data-management/ingestion-warnings/IngestionWarningsView.tsx.
posthog.com docs — the ingestion warnings page (https://posthog.com/docs/data/ingestion-warnings) if the warning is user-actionable.
v2 API / MCP descriptions — only if you added a new category or severity value; the example vocabularies live in the ingestion_warnings_v2 serializer help texts (posthog/api/ingestion_warnings_v2.py).

Warning-fixing skills (fixing-<warning-type>) that teach agents how to resolve each warning are planned under the ingestion warnings v2 effort; authoring one per new warning type will become part of this checklist.