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Runaway queries

Applies to: ✅ Microsoft Fabric ✅ Azure Data Explorer ✅ Azure Monitor ✅ Microsoft Sentinel

A runaway query is a kind of partial query failure that happens when some internal query limit was exceeded during query execution.

For example, the following error may be reported: HashJoin operator has exceeded the memory budget during evaluation. Results may be incorrect or incomplete.

There are several possible courses of action.

• Change the query to consume fewer resources. For example, if the error indicates that the query result set is too large, you can:
  • Limit the number of records returned by the query by
    • Using the take operator
    • Adding additional where clauses
  • Reduce the number of columns returned by the query by
    • Using the project operator
    • Using the project-away operator
    • Using the project-keep operator
  • Use the summarize operator to get aggregated data.

• Increase the relevant query limit temporarily for that query. For more information, see query limits - limit on memory per iterator. This method, however, isn't recommended. The limits exist to protect the Eventhouse and to make sure that a single query doesn't disrupt concurrent queries running on the Eventhouse.