What causes DF-AzureDataExplorer-ReadTimeout?

The Kusto query used as the source reads from a large table without time-range or partition filters, resulting in a query that runs longer than the connector timeout. The ADX cluster is under high concurrent load, causing query execution to slow significantly. The source table lacks an ingestion time or datetime partition column, preventing ADX from executing an efficient query plan

How do I fix DF-AzureDataExplorer-ReadTimeout?

Open the failing data flow in ADF Studio and inspect the Azure Data Explorer source transformation.. Add or tighten a datetime filter on the source query to limit the data volume per run — e.g., filter to the last N days instead of reading the full table.. Review the ADX cluster utilization in Azure Monitor during the data flow run window to check for capacity pressure.. If the query is complex, run it directly in the ADX query editor with .show queries to see the execution plan and identify slow operations.. Consider increasing the read timeout value in the ADF linked service if the query is inherently slow but not reducible.

Medium severitydata flow

Power BI Refresh Error:
DF-AzureDataExplorer-ReadTimeout

What does this error mean?

The ADF Mapping Data Flow Azure Data Explorer (ADX/Kusto) connector timed out while reading data. The Kusto query took longer than the connector's read timeout threshold, causing the data flow run to fail.

Common causes

1The Kusto query used as the source reads from a large table without time-range or partition filters, resulting in a query that runs longer than the connector timeout
2The ADX cluster is under high concurrent load, causing query execution to slow significantly
3The source table lacks an ingestion time or datetime partition column, preventing ADX from executing an efficient query plan

How to fix it

1Open the failing data flow in ADF Studio and inspect the Azure Data Explorer source transformation.
2Add or tighten a datetime filter on the source query to limit the data volume per run — e.g., filter to the last N days instead of reading the full table.
3Review the ADX cluster utilization in Azure Monitor during the data flow run window to check for capacity pressure.
4If the query is complex, run it directly in the ADX query editor with .show queries to see the execution plan and identify slow operations.
5Consider increasing the read timeout value in the ADF linked service if the query is inherently slow but not reducible.

Frequently asked questions

How do I find out how long my ADX query is taking?

Run the query in the ADX web UI (dataexplorer.azure.com) with the same parameters. Check execution time in the results pane, or use '.show queries' in Kusto to see recent execution times.

Can I increase the read timeout without changing the query?

Yes — the ADF ADX linked service has a timeout property that can be increased. However, the better fix is filtering the source query so it reads less data per execution.

Does this error mean my ADX cluster is too small?

Not necessarily — timeouts are often caused by reading too much data without filters, not by cluster size. Profile the query before scaling up the cluster.

Official documentation: https://learn.microsoft.com/en-us/azure/data-factory/data-flow-troubleshoot-guide