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Type: Question
Resolution: Duplicate
Priority: Minor - P4
Fix Version/s: None
Affects Version/s: 3.6.3
Component/s: Write Ops
Labels:
- SWKB
Environment:

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hw: AWS c4.2xlarge
operating system: Ubuntu xenial
kernel: 4.4.0-92-generic #115-Ubuntu SMP Thu Aug 10 09:04:33 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
mongodb volume: 130GiB io1 1000 IOPS

conf:
storage:
  dbPath: /data/data
  journal:
    enabled: true
  engine: wiredTiger

systemLog:
  destination: file
  logAppend: true
  path: /data/log/mongod.log

net:
  port: 27017
  bindIp: 0.0.0.0

replication:
  oplogSizeMB: 512
  replSetName: foo

operationProfiling:
  slowOpThresholdMs: 1
  mode: off

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hw: AWS c4.2xlarge operating system: Ubuntu xenial kernel: 4.4.0-92-generic #115-Ubuntu SMP Thu Aug 10 09:04:33 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux mongodb volume: 130GiB io1 1000 IOPS conf: storage:   dbPath: /data/data   journal:     enabled: true   engine: wiredTiger systemLog:   destination: file   logAppend: true   path: /data/log/mongod.log net:   port: 27017   bindIp: 0.0.0.0 replication:   oplogSizeMB: 512   replSetName: foo operationProfiling:   slowOpThresholdMs: 1   mode: off

Yesterday I upgraded one of our 3.4 mongodb cluster to 3.6 (3.4.9 -> 3.6.3).
After upgrade I noticed increased write IO (IOPS and throughput).
Added also 2 screenshots, upgrade was done at 5:20.

When looking with iotop, I can see WTOplog.lThread is writing a lot, does it mean that 3.6 writes more oplog? Is it something that is expected or is it regression?