Cassandra read write latency for large partition

Question

For a large cassandra partition read latencies are usally huge. But does write latency get impacted in this case? Since cassandra is columnar database and holds immutable data, shouldn't the write (which appends data at the end of the row) take less time?

Answer 1

In all the experiments I have conducted with Cassandra, I have noticed that write throughput is not affected by data size while read performance takes a big hit if your SSTables are too big, concurrent_reads threads are low ( check using nodetool tpstats if ReadStage is going into pending state) and increase them in cassandra.yaml file. Using LeveledCompaction seems to help as data for same key remains in same SSTable. Make sure your data is distributed evenly across all nodes. Cassandra optimization is tricky and you may have to implement "hacks" to obtain desired performance in minimum possible hardware.