Increased CPU usage after upgrading from 3.0 to 3.2

[Emil Burzo]

Hey,

I've recently upgraded a replica set from Ubuntu 14.04 to 16.04, and with that, MongoDB from 3.0 to 3.2.

After the upgrade I'm seeing:

• increased CPU usage on the two hosts that have SSD's
  
• increased CPU and IOWAIT on the host that has regular HDDs (in software RAID1, if it makes any difference)

The workload hasn't changed before/after the upgrade (about 40-60 inserts / 1-2 queries / 0 updates / 0 deletes -- per second)

The configuration also hasn't changed, I've been running WiredTiger before as well.

The storage configuration is configured as follows:

storage:
  dbPath: /var/lib/mongodb
  directoryPerDB: true
  journal:
    enabled: true
  engine: "wiredTiger"
  wiredTiger:
        engineConfig: 
            journalCompressor: zlib
        collectionConfig: 
            blockCompressor: zlib 
        indexConfig:
            prefixCompression: true

I've attached some munin graphs from the three hosts where the difference should be pretty visible.

Thoughts?

Thanks for reading.

- Emil

[ra...@quantumgraph.com]

Hi All,
I also have observerd increase in CPU usage when upgraded from 3.2.6 to 3.2.9

General trend is displayed and when we updated we have constant spike in cpu usage for 1 continuous day.

Thanks,
Ravi