Never index unbounded fields such as UUIDs, session tokens, or raw URLs in the primary dimension or tag schema; store them as non-indexed payload columns instead. Apply hashing or bucketing to continuous numeric dimensions, partition on low-cardinality fields such as region and environment, and enforce schema-at-write validation to reject unexpected high-cardinality fields before they propagate into the index. Pre-aggregation before write further reduces the unique series count that storage systems must manage.