Metric chart with aggFn increase and a multi-column group-by fails: toString() gets several arguments #3477

What happened?

A metric chart on a Sum metric with aggFn: increase and a group-by of two or more columns, given as a comma-separated string, fails with:

An incorrect number of arguments was specified for function 'toString'. Expected 1 argument, got 2 arguments: In scope SELECT tuple(Attributes['destination_service_name'], Attributes['response_code']) AS group, sum(Rate) AS bucket_value FROM Bucketed WHERE (Attributes['destination_service_name'], ((Attributes['response_code']) IS NOT NULL) AND (toString(Attributes['destination_service_name'], Attributes['response_code']) != '')) GROUP BY group, __hdx_time_bucket2.

Expected: one series per (destination_service_name, response_code) pair, the same as with a single group-by column.

What we checked on the same metric and time range:

• increase with one group-by column works.
• sum with the same two-column group-by works.
• increase with two columns fails both with Map expressions (Attributes['a'], Attributes['b']) and with plain MATERIALIZED columns (`col_a`, `col_b`).

As far as we can tell, the cause is in the top-N ranking added for increase + group-by (packages/common-utils/src/core/renderChartConfig.ts at 7752c88):

• renderSelectList returns a string group-by as a single ChSql (if (typeof selectList === 'string') return chSql\${{ UNSAFE_RAW_SQL: selectList }}``): https://github.com/hyperdxio/hyperdx/blob/7752c880e0f2d96be8926af71beebdf0b1e7d4b6/packages/common-utils/src/core/renderChartConfig.ts#L733-L741
• The increase path then treats that single fragment as one column. groupByEmptyFilter wraps the whole a, b in (… IS NOT NULL AND toString(…) != ''): https://github.com/hyperdxio/hyperdx/blob/7752c880e0f2d96be8926af71beebdf0b1e7d4b6/packages/common-utils/src/core/renderChartConfig.ts#L2341-L2362
• The series-limit CTE handles the same case by splitting a string group-by with splitAndTrimWithBracket first: https://github.com/hyperdxio/hyperdx/blob/7752c880e0f2d96be8926af71beebdf0b1e7d4b6/packages/common-utils/src/core/renderChartConfig.ts#L1605-L1614

Splitting the string group-by the same way before building groupByEmptyFilter should fix it. The tuple(${groupBySql}) parts already work with the comma-separated form.

Steps to reproduce

Reproduces on play.hyperdx.io? Didn't try. We hit it through the MCP tools on our own deployment.

1. Use a Metric source whose sum table has a counter with two attributes, for example Istio's istio_requests_total (destination_service_name, response_code).
2. Call the MCP tool clickstack_table with:
   • select: [{"aggFn": "increase", "metricType": "sum", "metricName": "istio_requests_total"}]
   • groupBy: "Attributes['destination_service_name'], Attributes['response_code']"
3. It fails with the error above.
4. Change aggFn to sum, or drop the second group-by column. It works.

We haven't checked the UI chart editor. It renders through the same renderChartConfig, so we expect a two-column group-by on an increase chart to fail the same way there.

How are you running HyperDX?

Helm (ClickStack chart 2.1.0) with the hyperdx:2-nightly image, which is 2.42.0 plus the Node bump from #3456. Our own ClickHouse 26.2.5.45.

Where does it show up?

The API: the MCP tool clickstack_table.

Debug info

N/A. We saw this through the API's MCP tools, not the UI.

Logs

The error is quoted above.

Written with help from an AI assistant (Claude Code). The behaviour and the error come from our own deployment.