Subject: [mongodb-user] Re: Vzise vs res across replicaset

Hi Max

I am wondering why is there this difference between the vsize/res of the 2nd secondary and the 1st one?

It’s quite hard to tell without some in-depth logging data and long-term metrics data. However, there may be some hints as to what happened.

  • Are you using bare metal hardware, or is it provisioned using a cloud provider?
  • If it’s a cloud provider, which one is it?
  • How many mongod are running inside a single machine?
  • What are the output of db.serverCmdLineOpts() from each of the three nodes?
  • What are the output of rs.status() and rs.conf()?
  • Is your application using a majority read concern?
  • Are the real-time clocks reliable across the three machines?
  • Is there a particular difference of the 3rd node vs. the other two? e.g., is it on a different datacenter?
  • Are you doing a secondary read, e.g. for analytical purposes?
  • Have you tried restarting the affected secondary, and see the issue manifest itself again?
  • Have you tried upgrading to 3.4.6? There may be some issue that was fixed.

Having said that, please understand that there may not be a definitive answer exists for your question.

Best regards,

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