Overview: The following query does not use the existing instance_hrid_idx_unique index.
Without the index being applied it's very slow and often ends with timeout exception on DB side. In a 8M records instance table, it takes 3 minutes to return result. It seems like the CQL query string may need the "==" sign to search for hrid's by using the existing instance-hrid unique index. If this change in the code is not possible, a FT index may need to be created to make the query's execution speed acceptable. But this FT index takes about 800ms+ to execute, which is about 8x slower than if it was using the unique index. Therefore, update the code to use the unique hrid index.