nosql-expert

List all access patterns first, then store multiple entity types in one table using composite keys like USER#123 as the partition key and PROFILE or ORDER#998 as sort keys. This lets one query fetch related entities together in a single request.

Query-first modeling means designing tables around specific access patterns rather than entities. You list every query your application needs, then create tables or indexes that serve each pattern with a single lookup, since joins are not available.

Both use partition keys and sort keys, but Cassandra uses clustering columns with CQL while DynamoDB uses GSIs and LSIs for alternate views. DynamoDB adds capacity modes (WCU/RCU) and TTL; Cassandra requires avoiding ALLOW FILTERING and tombstone-heavy deletes.

Hot partitions occur when the partition key has low cardinality, such as status or gender, concentrating traffic on one physical node. Use high-cardinality keys like user IDs or composite keys to spread data and traffic evenly across partitions.

ALLOW FILTERING should never appear in production queries because it triggers a full cluster scan. Its presence indicates the data model does not match the query pattern, so redesign the table or add a purpose-built table instead.