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  1. Core Server
  2. SERVER-23622

Inconsistent throughput during insert workload



    • Bug
    • Status: Closed
    • Major - P3
    • Resolution: Done
    • None
    • None
    • WiredTiger
    • None
    • Fully Compatible
    • ALL


      With a heavy insert load and a secondary that is delayed the cache on the primary fills to 100% and operation rates drop. Here's a run showing behavior on the primary with the secondary delayed due to lag, but a similar effect is seen if the secondary is intentionally delayed using slaveDelay.

      • from D-E the cache is 95% full and insert rate drops considerably, possibly due to application threads doing evictions?
      • F-G and H-I seem to be seem to be related to checkpoints, possibly also in combination with the full cache?
      • the rate of pages walked for eviction is generally very high, about 6k times the rate of pages actually evicted, suggesting that the issue is difficulty finding pages to evict to keep the cache at target levels

      The high rate of pages walked for eviction suggests a connection to SERVER-22831, which also showed that symptom in connection with a full cache; however the above run was on 3.2.5-rc1 where SERVER-22831 was fixed, so it seems there is a different issue here.

      The above test involved

      • 3.2.5-rc1
      • 2-node replica set
      • 25 GB cache
      • 100 GB oplog
      • 5 threads inserting 800 byte documents into 5 separate collections

      for t in $(seq 5); do
          mongo --eval "
              x = ''
              for (var i=0; i<800; i++)
                  x += 'x'
              docs = []
              for (var i=0; i<1000; i++)
              ops = [{
                  op: 'insert',
                  ns: 'test.c' + '$t',
                  doc: docs,
              res = benchRun({
                  ops: ops,
                  seconds: 10000,
                  parallel: 1
          " &


        1. 23622.0901.tar.gz
          728 kB
          Susan LoVerso
        2. 23622.20.tar.gz
          1013 kB
          Susan LoVerso
        3. 23622.nolog.tar.gz
          428 kB
          Susan LoVerso
        4. 23622.results.tar.gz
          868 kB
          Susan LoVerso
        5. 2816.20.tar.gz
          392 kB
          Susan LoVerso
        6. aggressive.43min.tar.gz
          671 kB
          Susan LoVerso
        7. cs29611.png
          127 kB
          Bruce Lucas
        8. diagnostic.data.tar
          146 kB
          Bruce Lucas
        9. exp.tar.gz
          414 kB
          Susan LoVerso
        10. lagging.png
          370 kB
          Bruce Lucas
        11. patch.png
          223 kB
          Bruce Lucas
        12. patch-diagnostic.data.tar
          532 kB
          Bruce Lucas
        13. run8.tar.gz
          331 kB
          Susan LoVerso
        14. run8-zoom.png
          229 kB
          Susan LoVerso
        15. run-branch.png
          274 kB
          Susan LoVerso
        16. stalls.png
          104 kB
          Bruce Lucas

        Issue Links



              sue.loverso@mongodb.com Susan LoVerso
              bruce.lucas@mongodb.com Bruce Lucas
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