Since you asked about long term storage and occasional queries, have you considered offloading to the cloud? (Disclosure: I work for Google) With BigQuery you

Since you asked about long term storage and occasional queries, have you considered offloading to the cloud? (Disclosure: I work for Google) With BigQuery you can: - Store as much relational data as you want ($20->$10 per terabyte per month). - Query it whenever, and get charged only by query (no servers needed) - To stay on topic: HyperLogLog: https://cloud.google.com/bigquery/docs/reference/standard-sql/functions-and-operators#hyperloglog-functions https://cloud.google.com/bigquery/docs/reference/standard-sq... Note that BigQuery exposes partial HLL functions like HLL_COUNT.INIT, HLL_COUNT.MERGE, HLL_COUNT.MERGE_PARTIAL, and HLL_COUNT.EXTRACT. "These functions operate on sketches that compress an arbitrary set into a fixed-memory representation. The sketches can be merged to produce a new sketch that represents the union, before a final estimate is extracted from the sketch."