Gram Telemetry Query Dimensions

What this covers

telemetry.query (POST /rpc/telemetry.query) is a generic, org-scoped analytics endpoint. It groups pre-aggregated usage metrics by an allowlisted dimension and filters on those same dimensions. This skill explains how to add a new dimension (a new attribute value to group/filter by).

Dimensions vs. measures. A dimension is a breakdown/filter axis (department_name, model, role). A measure is a number being aggregated (total_cost, total_tokens). This skill is about dimensions only. Adding a new measure is a different (parallel) path through the same files — queryMeasures, attributeMeasureSelects, AttributeMetricsMeasures, QueryMeasures.

Everything is backed by one ClickHouse AggregatingMergeTree, attribute_metrics_summaries, fed by attribute_metrics_summaries_mv. Each dimension is one column on that table. The query layer never sees raw JSON paths or SQL from clients — dimensions are a closed allowlist validated at three layers that must stay in sync.

Activate the clickhouse skill (schema/MV work) and golang skill (repo/service edits) alongside this one.

The four layers (keep them in sync)

A dimension key like department_name must appear in all four places. Adding a new one means touching each:

dimension_values (the per-group distinct-value lists on each QueryRow) is automatic — it iterates attributeDimensionRegistry, so a new dimension shows up there with no extra code.

Pick the dimension kind

The repo classifies every dimension as one of three attributeDimensionKinds. This drives how it is grouped and filtered:

• attributeDimScalar — one string value per row (e.g. department_name, model). Group: plain column. Filter: IN.
• attributeDimArray — Array(String), multiple values per user/row (e.g. roles, groups). Group: arrayJoin() (attributes spend to each element). Filter: hasAny(). Stored intact in the sorting key (one array per row) so it does not multiply row count.
• attributeDimProject — the gram_project_id UUID key column; grouped via toString().

Most new identity/request attributes are scalar. Use array only when the attribute is genuinely list-valued per user.

Cardinality. The MV stays cheap because every scalar dimension is functionally determined by the user (one department, one job title per user), so adding one does not multiply rows. Do not add a high-cardinality, per-event scalar (e.g. a raw request id) as a dimension — it would explode the aggregate.

Step-by-step

1. ClickHouse schema + migration

Edit server/clickhouse/schema.sql. For a scalar dimension foo derived from a log attribute attributes.user.attributes.foo:

1. Add the column to the attribute_metrics_summaries table:

   foo String,
   

2. Add the derived SELECT to attribute_metrics_summaries_mv and the column to its GROUP BY:

   -- in the SELECT list
   toString(attributes.user.attributes.foo) AS foo,
   -- ...and in GROUP BY
   GROUP BY gram_project_id, time_bucket, department_name, ..., foo;
   

   (Array dimensions use CAST(attributes.user.foo AS Array(String)) AS foo. If a materialized column already exists on telemetry_logs — e.g. user_email, hook_source — reference it directly instead of re-deriving from JSON.)
3. Add the column to the table's ORDER BY sorting key (scalar columns slot in with the other identity dimensions; array columns go at the end alongside roles, groups). The sorting key keeps cardinality bounded.

Then generate the migration (this is a ClickHouse migration, governed by the same expand/contract rules as Postgres — see the migration rules in CLAUDE.md):

mise clickhouse:diff add-foo-attribute-dimension

Atlas diffs schema.sql and emits the migration into server/clickhouse/migrations/ (and the golang-migrate copy), then auto-runs clickhouse:gen-materialized-cols. Never hand-edit the generated migration or atlas.sum.

MV recreation + backfill. Changing the MV's SELECT/GROUP BY and the table sorting key makes Atlas drop and recreate the MV. The MV only transforms rows ingested after it exists — historic rows are not re-aggregated, so the new column reads empty ('') for old buckets. That is acceptable (data ages out at the 30-day TTL); call it out in the PR. Run migrations against local DBs only.

2. Goa design allowlist

In server/design/telemetry/design.go, add the public key to queryDimensions:

var queryDimensions = []any{
    "department_name",
    // ...
    "foo", // <-- new
}

This single slice feeds the Enum(...) on both QueryPayload.group_by and QueryFilter.dimension, so the new key becomes a valid group-by and filter value automatically. (The public key need not equal the column name — email maps to user_email.)

3. Repo registry

In server/internal/telemetry/repo/attribute_metrics.go, add the mapping to attributeDimensionRegistry (public key → safe column expression + kind):

var attributeDimensionRegistry = map[string]attributeDimension{
    // ...
    "foo": {column: "foo", kind: attributeDimScalar},
}

This is the only place a key maps to a real column, and it is what keeps client input from ever reaching SQL as a raw path. The registry powers grouping, filtering, and the dimension_values map — so once it's here, the new dimension's distinct values automatically appear in every group's dimension_values.

Keep queryDimensions (design) and attributeDimensionRegistry (repo) in sync. A key in the Enum without a registry entry returns unknown group_by/filter dimension at runtime; a registry entry not in the Enum is unreachable.

4. Regenerate + verify

mise gen:goa-server   # regenerate Goa types/openapi from the design
mise gen:sdk          # regenerate the TypeScript SDK from the OpenAPI spec

Then:

mise build:server
mise lint:server
aube run -F dashboard type-check

5. Tests

• Unit (query_internal_test.go): buildQueryResult is dimension-agnostic; add coverage only if you changed rollup behavior.
• Integration (query_test.go, requires ClickHouse): insertAttributeUsageLog writes a telemetry row. Add your attribute to the inserted JSON, then assert the new dimension groups/filters and appears in dimension_values. Group-by assertions wait on require.Eventually because the MV is eventually consistent.

mise run test:server ./internal/telemetry/ -run TestQuery -count=1

Gotchas

• Sorting-key drift. The migration's ORDER BY must match schema.sql exactly, or Atlas will want to rebuild the table. Let clickhouse:diff generate it; don't hand-write.
• Empty values are filtered. dimension_values drops '', so unset attributes show as an empty list. Grouping by a dimension where the attribute is unset surfaces under the '' group (and array dimensions map an empty array to a single '' element so role-less spend isn't dropped).
• Don't add measures here. If the request is really "expose a new number to aggregate," that's the measures path, not a dimension.
• Aggregate read combinators. Measure columns are *If aggregate states and must be read with the matching *IfMerge combinators (see attributeMeasureSelects). Dimensions are plain columns and need none of this.