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Troubleshoot TestData data source issues

This document provides solutions to common issues you may encounter when using the TestData data source. TestData is a built-in data source with no external dependencies, so most issues relate to scenario configuration or data formatting.

Query errors

These errors occur when running TestData scenarios.

“No data” or empty panels

Symptoms:

• Panel displays “No data” message.
• Query executes without error but returns nothing.

Possible causes and solutions:

Unexpected error from Conditional Error

Symptoms:

• Query returns a server error or panic message.
• Error appears immediately when running the query.

Solutions:

1. The Conditional Error scenario triggers a server panic when the String Input field is empty. This is the intended behavior for error testing.
2. To return data instead of an error, populate the String Input field with comma-separated values (for example, 1,20,90,30,5,0).
3. To change the error type, use the Error type drop-down to select between Server panic, Frontend exception, and Frontend observable.

Error with source returns an error

The Error with source scenario intentionally returns errors for testing how Grafana handles different error sources. This isn’t a misconfiguration.

• Plugin error source simulates an error originating from the plugin itself.
• Downstream error source simulates an error from a downstream service.

Use this scenario to test alerting rules, error displays, and error handling in custom panels.

Slow Query appears stuck

Symptoms:

• Query runs for an extended period.
• Panel shows a loading spinner indefinitely.

Solutions:

1. Check the String Input field, which controls the delay duration. The default is 5s.
2. Reduce the value to a shorter duration (for example, 1s or 500ms).
3. The field accepts Go duration syntax: 5s (seconds), 1m (minutes), 500ms (milliseconds).

Wrong data type for the visualization

Symptoms:

• Panel shows “Data does not have a time field” or similar type mismatch errors.
• Visualization renders but looks wrong (for example, a table when you expected a graph).

Solutions:

1. Match the scenario to the visualization type. For example, use the Logs scenario with the Logs panel, Node Graph with the Node Graph panel, and Trace with the Traces panel.
2. Time-series panels require scenarios that produce time-series data (Random Walk, Predictable Pulse, CSV Metric Values, Predictable CSV Wave).
3. For table panels, use Table Static, Random Walk Table, or CSV File.

Predictable Pulse pattern doesn’t match expectations

Symptoms:

• The on/off pattern doesn’t align with expected times.
• Values appear at unexpected intervals.

Solutions:

1. Predictable Pulse aligns timestamps to the step interval based on absolute time from the epoch, not from the start of the time range. This means the pattern starts at the same point regardless of when you load the dashboard.
2. Verify the cycle duration matches your intent: the full cycle is Step * (On Count + Off Count) seconds.
3. Check that On Value and Off Value are set correctly. The defaults are 2 and 1, not 1 and 0.

CSV and data input errors

These errors occur with scenarios that accept user-provided data.

CSV Content or CSV Metric Values return unexpected results

Symptoms:

• Data doesn’t match expectations.
• Fewer data points than expected.
• Parsing errors.

Solutions:

1. Verify CSV formatting: headers in the first row, commas as delimiters, numeric values unquoted.
2. For CSV Metric Values, enter only comma-separated numbers in the String Input field (for example, 1,20,90,30,5,0).
3. The special values null and nan are supported in Predictable CSV Wave values. Use null for missing data points and nan for Not-a-Number values.
4. Check for trailing commas or extra whitespace in your input.

Raw Frames JSON parse errors

Symptoms:

• Error message about invalid JSON.
• Panel fails to render.

Solutions:

1. Validate that the JSON matches the Grafana data frame format.
2. Use the paste helpers in the editor to import data from panel JSON or raw query results.
3. Verify that field types are consistent within each field array.

Streaming errors

These errors occur with the Streaming Client and Grafana Live scenarios.

Streaming Client doesn’t update

Symptoms:

• Panel shows initial data but doesn’t update.
• No new data points appear over time.

Solutions:

1. Verify the Speed field is set to a reasonable value (in milliseconds). Lower values produce faster updates.
2. For the Fetch type, verify the URL is accessible from the browser.
3. Check the browser console for WebSocket or network errors.

Grafana Live channel shows no data

Symptoms:

• Panel remains empty after selecting a channel.
• No streaming data appears.

Solutions:

1. Confirm the selected channel matches one of the available options: random-2s-stream, random-flakey-stream, random-labeled-stream, or random-20Hz-stream.
2. Verify that Grafana Live is enabled in your Grafana instance.
3. Check the Grafana server logs for Live connection errors.

Template variable errors

These errors occur when using TestData with dashboard template variables.

Variable drop-down is empty

Symptoms:

• Variable drop-down shows no options.
• Preview in the variable editor returns zero values.

Solutions:

1. Verify the query string navigates valid nodes in the metric tree. Use * to return all top-level nodes.
2. Check that dot-separated path segments match the tree structure (for example, A.* returns children of node A). An invalid path like Z.* returns nothing because Z doesn’t exist in the tree.
3. Verify the TestData data source is selected in the variable editor.
4. Click Run query in the variable editor preview to test.

Chained variable doesn’t update

Symptoms:

• A dependent variable (for example, $region.*) doesn’t refresh when the parent variable changes.
• The drop-down shows stale values from a previous selection.

Solutions:

1. Set the dependent variable’s Refresh option to On dashboard load or On time range change in the variable editor.
2. Verify the query uses the correct parent variable syntax (for example, $region.* not region.*).

Variable value not interpolated in queries

Symptoms:

• Panel shows the literal string $varname instead of the variable value.
• Labels or data don’t change when the variable selection changes.

Solutions:

1. Verify you’re using the correct variable syntax: $varname or ${varname}.
2. TestData interpolates variables in these fields only: Labels, Alias, Scenario, String Input, CSV Content, and Raw Frame Content. Other fields don’t support variable substitution.

Alerting errors

These errors occur when using TestData with Grafana Alerting.

Alert rule shows “no data” unexpectedly

Symptoms:

• Alert rule status shows No Data even though the scenario works in a panel.
• Alert never transitions to firing or normal.

Solutions:

1. Verify you’re using a backend-evaluated scenario. Browser-only scenarios (Streaming Client, Grafana Live, Grafana API, Steps, No Data Points) return empty results when evaluated by the alerting engine. Use a backend scenario like Random Walk or Predictable Pulse instead.
2. Confirm the scenario is returning time-series data. Scenarios that produce logs (Logs), traces (Trace), graphs (Node Graph, Flame Graph), or tables (Table Static) can’t be used as alert conditions.
3. Check that the String Input field isn’t empty for scenarios that require it (for example, CSV Metric Values).

Alert rule never fires

Symptoms:

• Alert rule stays in Normal state.
• Data is visible in the panel but the alert condition is never met.

Solutions:

1. If using Random Walk, the values are non-deterministic and may not exceed your threshold. Use Predictable Pulse or CSV Metric Values with values that reliably cross the threshold.
2. Verify the Reduce expression is aggregating correctly. For example, Last returns the most recent value, while Mean averages the series.
3. Check the Threshold expression. Click Preview in the alert rule editor to see the evaluated value.
4. Ensure the evaluation interval is long enough for the scenario to produce data points. A Predictable Pulse with Step=60 needs at least a 60-second evaluation window.

Template variables don’t resolve in alert rules

Symptoms:

• Alert rule error mentions unresolved variables.
• Alert query uses $varname syntax but the variable isn’t replaced.

Solutions:

Grafana evaluates alert rules on the backend without dashboard context. Template variables like $varname aren’t resolved during alert evaluation. Replace variable references with fixed values in the scenario options.

For more information, refer to the alerting limitations.

Alert evaluation timeout

Symptoms:

• Alert rule transitions to Error state.
• Logs show a timeout during query evaluation.

Solutions:

1. If you’re using the Slow Query scenario, reduce the delay in the String Input field to a value shorter than the evaluation interval.
2. For other scenarios, verify that the query isn’t producing an excessive number of data points. Reduce the time range or increase the step interval.

Enable debug logging

To capture detailed error information for troubleshooting:

1. Set the Grafana log level to debug in the configuration file:

   ini Copy

   [log]
   level = debug

2. Review logs in /var/log/grafana/grafana.log (or your configured log location).

3. Look for entries containing testdata or testdatasource for scenario-specific details.

4. Reset the log level to info after troubleshooting to avoid excessive log volume.

Get additional help

If you’ve tried the solutions in this document and still encounter issues:

1. Check the Grafana community forums for similar issues.
2. Review Grafana GitHub issues for known bugs.
3. When reporting issues, include:
   • Grafana version
   • Selected scenario and its configuration
   • Error messages (redact sensitive information)
   • Steps to reproduce