Tables metrics recommendations 

Recommendations for assistance with troubleshooting table performance issues.

Recommendations for assistance with troubleshooting table performance issues appear in the Recommendations panel when the Performance Service detects known issues in the table metrics.
Recommendation Description
Compaction Strategy Choose the compaction strategy that best fits your data and environment. Learn more about compaction strategies. The compaction strategy you use should be based on your data and environment. This Best Practice rule is set to run so that you are aware of the importance of choosing a compaction strategy. If you have already chosen the correct compaction strategy based on your environment, please disable this rule if you do not want to see a reminder about compaction strategy again.
Secondary indexes cardinality Checks for secondary indexes with too many distinct values. High cardinality secondary indexes can have a negative impact on system performance. Consider denormalizing the indexed data.
Tombstones count Number of tombstones processed during reads. Too many tombstones can cause a degradation of performance, which can even lead to query failures. Consider updating your data model to decrease the amount of deleted data. For TTLed time series data, consider reducing gc_grace_seconds and evaluating different compaction strategies.
Wide partitions Checks for excessively wide partitions. Excessively wide partitions have a negative impact on performance and are not recommended. Consider remodeling your data to break up wide partitions. A partition is considered to be wide when the size is greater than 100 MB.