You are not reading the latest stable version of this documentation. If you want up-to-date information, please have a look at 3.10.

CQL queries are not balanced among shards

For optimal performance, data and queries should be distributed evenly across nodes and shards. If some shards are getting more traffic they could become a bottleneck for Scylla.

There could be multiple explanations for these performance issues: data-model, non-prepared statement, or driver.

Blog post link