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  1. Core Server
  2. SERVER-31679

Increase in disk i/o for writes to replica set

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Details

    • Bug
    • Status: Closed
    • Major - P3
    • Resolution: Fixed
    • 3.6.0-rc0
    • 3.6.6, 3.7.3
    • Replication, Storage
    • Fully Compatible
    • ALL
    • v3.6
    • Storage 2018-02-12, Storage NYC 2018-03-12

    Description

      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.

      Attachments

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          io.png
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        Issue Links

          is duplicated by

          Question - SERVER-33537 High write IO after 3.6 upgrade

          • Minor - P4 - Minor loss of function, or other problem where easy workaround is present.
          • Closed
          is related to

          Bug - A problem which impairs or prevents the functions of the product. SERVER-33812 First initial sync oplog read batch fetched may be empty; do not treat as an error.

          • Critical - P2 - Crashes, loss of data, severe memory leak.
          • Closed

          Improvement - An improvement or enhancement to an existing feature or task. WT-3531 Provide a way to flush the log if commits were out of timestamp order

          • Major - P3 - Major loss of function.
          • Backlog
          related to

          Bug - A problem which impairs or prevents the functions of the product. SERVER-36221 [3.6] Performance regression on small updates to large documents

          • Major - P3 - Major loss of function.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. SERVER-37233 Increase in disk i/o for writes to replica set

          • Major - P3 - Major loss of function.
          • Closed

          Activity

            People

              geert.bosch@mongodb.com Geert Bosch
              bruce.lucas@mongodb.com Bruce Lucas (Inactive)
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              Dates

                Created:
                Updated:
                Resolved: