[CASSANDRA-13896] Improving Cassandra write performance

• Type: Improvement
• Status: Open
• Priority: Normal
• Resolution: Unresolved
• Fix Version/s: 5.x
• Component/s: Legacy/Local Write-Read Paths
• Labels: Performance

Environment

Skylake server with 2 sockets, 192GB RAM, 3xPCIe SSDs
OS: Centos 7.3
Java: Oracle JDK1.8.0_121

• Assignee: Unassigned
• Reporter: Prince Nana Owusu Boateng
• Created: 22/Sep/17 18:59
• Updated: 07/Mar/23 10:54

Description

During our Cassandra performance testing, we see high percentage of the CPU spent in org.apache.cassandra.utils.memory.SlabAllocator.allocate(int, OpOrder Group) * method. Appears to be high contention of the *<nextFreeOffset> atomic Integer in write workloads. This structure is used by the threads for keeping track of the region bytebuffer allocation. When the contention appears, adding more clients, modifications of write specific parameters does not change write throughput performance. Attached are the details of Java Flight Recorder (JFR), showing hot functions and also performance results. When we see this contention, we still have plenty of CPU and throughput left ( <20% Total average CPU utilization and <11% of the storage write total throughput). This occurs on Cassandra 3.10.0-src version using the Cassandra-Stress.

Proposal:
We will like to introduce a solution which eliminates the atomic operations on the <nextFreeOffset> atomic Integer. This implementation will allow concurrent allocation of bytebuffers without an atomic compareAndSet and incrementAndGet operations. The solution is expected to increase overall write performance while improving CPU utilization.