https://druid.apache.org/docs/latest/querying/groupbyquery.html#memory-tuning-and-resource-limits There's not a general rule for setting the size to spill to disk - it depends on query sizes. If it's currently not set, the default is 0, meaning there's no spill. I've seen a recommendation to try 10G, but note that any setting is per query, so you need sufficient disk space to accommodate the spill for as many concurrent groupBy queries as you might have. (This could theoretically be up to druid.server.http.numThreads * druid.query.groupBy.maxOnDiskStorage.) We do have an article mentioning this and other possible settings for large result sets in below article which mentions the 10G recommendation. I'd use caution with the other recommendations, though, and only set them as needed. Each configuration change has its own effects and ramifications, and can lead to issues in other areas. Try increasing maxOnDiskStorage with 2 to 3Gb first https://support.imply.io/hc/en-us/articles/360034310953-Tuning-Druid-for-Large-Result-Sets