[CASSANDRA-19429] Remove lock contention generated by getCapacity function in SSTableReader (original) (raw)

Profiling Cassandra 4.1.3 on large AWS instances, a high number of lock acquires is measured in the `getCapacity` function from `org/apache/cassandra/cache/InstrumentingCache` (1.9M lock acquires per 60 seconds). Based on our tests on r8g.24xlarge instances (using Ubuntu 22.04), this limits the CPU utilization of the system to under 50% when testing at full load and therefore limits the achieved throughput.

Removing the lock contention from the SSTableReader.java file by replacing the call to `getCapacity` with `size` achieves up to 2.95x increase in throughput on r8g.24xlarge and 2x on r7i.24xlarge:

Instructions to reproduce:

Requirements for Ubuntu 22.04

sudo apt install -y ant git openjdk-11-jdk

Build and run

CASSANDRA_USE_JDK11=true ant realclean && CASSANDRA_USE_JDK11=true ant jar && CASSANDRA_USE_JDK11=true ant stress-build  && rm -rf data && bin/cassandra -f -R

Run

bin/cqlsh -e 'drop table if exists keyspace1.standard1;' &&
bin/cqlsh -e 'drop keyspace if exists keyspace1;' &&
bin/nodetool clearsnapshot --all && tools/bin/cassandra-stress write n=10000000 cl=ONE -rate threads=384 -node 127.0.0.1 -log file=cload.log -graph file=cload.html &&
bin/nodetool compact keyspace1   && sleep 30s &&
tools/bin/cassandra-stress mixed ratio(write=10,read=90) duration=10m cl=ONE -rate threads=406 -node localhost -log file=result.log -graph file=graph.html