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From Bill Walters <>
Subject Elevated response times from all nodes in a data center at the same time.
Date Mon, 14 Oct 2019 23:10:26 GMT
Hi Everyone,

Need some suggestions regarding a peculiar issue we started facing in our
production cluster for the last couple of days.

Here are our Production environment details.

AWS Regions: us-east-1 and us-west-2. Deployed over 3 availability zone in
each region.
No of Nodes: 24
Data Centers: 4 (6 nodes in each data center, 2 OLTP Data centers for APIs
and 2 OLAP Data centers for Analytics and Batch loads)
Instance Types: r5.8x Large
Average Node Size: 182 GB
Work Load: Read heavy
Read TPS: 22k
Cassandra version: 3.0.15
Java Version: JDK 181.
EBS Volumes: GP2 with 1TB 3000 iops.

1. We have been running in production for more than one year and our
experience with Cassandra is great. Experienced little hiccups here and
there but nothing severe.

2. But recently for the past couple of days we see a behavior where our p99
latency in our AWS us-east-1 region OLTP data center, suddenly starts
rising from 2 ms to 200 ms. It starts with one node where we see the 99th
percentile Read Request latency in Datastax Opscenter starts increasing.
And it spreads immediately, to all other 6 nodes in the data center.

3. We do not see any Read request timeouts or Exception in the our API
Splunk logs only p99 and average latency go up suddenly.

4. We have investigated CPU level usage, Disk I/O, Memory usage and Network
parameters for the nodes during this period and we are not experiencing any
sudden surge in these parameters.

5. We setup client using WhiteListPolicy to send queries to each of the 6
nodes to understand which one is bad, but we see all of them responding
with very high latency. It doesn't happen during our peak traffic period
sometime in the night.

6. We checked the system.log files on our nodes, took a thread dump and
checked for any rouge processes running on the nodes which is stealing CPU
but we are able to find nothing.

7. We even checked our the write requests coming in during this time and we
do not see any large batch operations happening.

8. Initially we tried restarting the nodes to see if the issue can be
mitigated but it kept happening, and we had to fail over API traffic to
us-west-2 region OLTP data center. After a couple of hours we failed back
and everything seems to be working.

We are baffled by this behavior, only correlation we find is the "Native
requests pending" in our Task queues when this happens.

Please let us know your suggestions on how to debug this issue. Has anyone
experienced an issue like this before.(We had issues where one node starts
acting bad due to bad EBS volume I/O read and write time, but all nodes
experiencing an issue at same time is very peculiar)

Thank You,
Bill Walters.

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