Jeff Shaw created CASSJAVA-145:
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Summary: Reduce CPU cost of DefaultLoadBalancingPolicy query plans
Key: CASSJAVA-145
URL: https://issues.apache.org/jira/browse/CASSJAVA-145
Project: Apache Cassandra Java driver
Issue Type: Improvement
Reporter: Jeff Shaw
Assignee: Jeff Shaw
I have an application that I need to run insert queries as efficiently as
possible. Using a Java Flight Recorder profile of the Scylla client version
4.17.0, I found that DefaultLoadBalancingPolicy.newQueryPlan() used 38% of the
CPU time. This ticket aims to reduce that without changing the query plan
order. The Scylla client uses the Cassandra client as an upstream library, so I
want to do as much work as possible here first.
The first optimization I found is to avoid ArrayUtils.rotate()'s O(n^2)
implementation, where n is the number of live nodes in the local data center.
The way I think this could be done efficiently is to instead introduce a new
class that provides elements in the rotated order as they are requested. This
makes the worst case O(n), but many cases won't need to produce all n values.
A second optimization is to rewrite ArrayUtils.bubbleDown() and bubbleUp()
using System.arraycopy().
A third optimization in newQueryPlan() is to exit the replica scan once all
replicas are found.
Optionally, I thought maybe a good optimization would be to reorder the method
calls in isUnhealthy() to call isResponseRateInsufficient() first. With that
change, some calls to getInFlight() will be skipped.
Following are benchmark results for when a busy node has a sufficient response
rate in 4.x and then after a draft implementation for this ticket.
||node count||before (ns)||after (ns)||
|3|82|71|
|10|176|115|
|20|483|134|
|50|2460|197|
For 3 nodes, reordering isUnhealthy() causes some regressions when nodes aren't
busy: from 59 to 86 ns with an insufficient response rate, and from 57 to 73 ns
with a sufficient one.
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