Increase in disk i/o for writes to replica set

XMLWordPrintableJSON

    • Fully Compatible
    • ALL
    • v3.6
    • Storage 2018-02-12, Storage NYC 2018-03-12
    • None
    • 3
    • None
    • None
    • None
    • None
    • None
    • None

      Simple insert loop running against 1-node replica set

          db.c.insert({_id: 0, i: 0})
    for (i = 0; i < 100000; i++)
        db.c.update({_id: 0}, {$inc: {i: 1}})

      Shows a large increase in journal syncs, disk write requests, bytes written. 3.4.9 left, 3.6.0-rc0 right:

      It appears we're doing a flush on every update, even though there's no write concern. In the simple repro above this doesn't seem to affect performance (for reasons tbd) but with more complex workloads the additional journal i/o will impact performance.

      Does not reproduce with standalone mongod.

        1. four.png
          four.png
          73 kB
        2. io.png
          io.png
          160 kB
        3. io.png
          io.png
          188 kB

            Assignee:
            Geert Bosch
            Reporter:
            Bruce Lucas (Inactive)
            Votes:
            0 Vote for this issue
            Watchers:
            22 Start watching this issue

              Created:
              Updated:
              Resolved: