SSTables reduce read capacity because records might be spread across several SSTables, as a result of frequent write operations, modifications, and deletions.

1. Check the number of SSTables per column family (table) by using the nodetool tablestats command.
2. Analyze the outcome to determine the root cause of the issue.
   Depending on the nodetool tablestats outcome, you might want to perform such actions as adjusting your compaction throughput, expanding the memory size for file caching, and so on. For more information, see the Apache Cassandra documentation.