Uploaded image for project: 'Core Server'
  1. Core Server
  2. SERVER-42732

delayed replica performance downgrade

    XMLWordPrintable

    Details

    • Operating System:
      ALL

      Description

      Hi,

       

      beacuse of a mixture of hardware-servers and VMs, we are running a replicaset with 4 active members and 2 arbiters.

       

      Host1: Primary + arbiter

      Host2: Secondary + arbiter

      Host3: Secondary

      Host4: Secondary

       

      As soon as we configure a secondary to be a delayed and hidden replica, queries using the

      changeStream features clogg up the system until its unusable.

      Without the delayed replica these queries take < 100ms, with the delayed replica deployed these timings increase significantely up to multiple thousands of ms.

      Also the systemload is increasing heavily, from ~0.5 without delayed replica, up to observed 6.

       

      The documentation offers the following advice for PSA-Configurations (only if one has only 3 members in the replicaset: master-slave-arbiter):

      https://docs.mongodb.com/v3.6/reference/read-concern-majority/#disable-read-concern-majority

       

      But this should have no effect in our setup, as we still do have a fully functional PSS replication.

       

      After removing the delay and setting the replica to hidden=false the problems vanish and the system is stable and performant again.

       

      This is reproducible on our setup.

       

      We can

        Attachments

          Activity

            People

            • Votes:
              0 Vote for this issue
              Watchers:
              3 Start watching this issue

              Dates

              • Created:
                Updated:
                Resolved: