Re: Cassandra p95 latencies

[Abe Ratnofsky]

40ms is definitely higher than expected. Have you run your queries with TRACING enabled to see where the latency is coming from? https://docs.datastax.com/en/cql-oss/3.3/cql/cql_reference/cqlshTracing.html 40ms is also a fairly specific duration: https://eklitzke.org/the-caveats-of-tcp-nodelay > On Linux this can cause up to a 40 ms delay when acking packets — Abe On Aug 10, 2023, at 17:13, MyWorld <timeplus.1...@gmail.com> wrote:  Hi, P95 should not be a problem if rightly designed. Levelled compaction strategy further reduces this, however it consume some resources. For read, caching is also helpful.  Can you check your cpu iowait as it could be the reason for delay  Regards, Ashish On Fri, 11 Aug, 2023, 04:58 Shaurya Gupta, <shaurya.n...@gmail.com> wrote: Hi community What is the expected P95 latency for Cassandra Read and Write queries executed with Local_Quorum over a table with 3 replicas ? The queries are done using the partition + clustering key and row size in bytes is not too much, maybe 1-2 KB maximum. Assuming CPU is not a crunch ? We observe those to be 40 ms P95 Reads and same for Writes. This looks very high as compared to what we expected. We are using Cassandra 4.0. Any documentation / numbers will be helpful. Thanks -- Shaurya Gupta