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  1. WiredTiger
  2. WT-2260

Workloads evict internal pages unexpectedly

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Details

    • Bug
    • Status: Closed
    • Major - P3
    • Resolution: Done
    • None
    • WT2.7.0
    • None
    • None

    Description

      We have noticed that some workloads are evicting internal pages when there are other candidates available.

      A wtperf configuration that results in internal page eviction, when there is plenty of space in cache for the internal structure is:

      conn_config="statistics=[all],statistics_log=(wait=10),cache_size=4G,eviction_trigger=85,eviction_target=70,eviction_dirty_trigger=85,eviction_dirty_target=60"
      table_config="type=file,allocation_size=4KB,internal_item_max=1433,internal_key_truncate=true,internal_page_max=16KB,leaf_item_max=1433,leaf_page_max=4KB,prefix_compression=false,split_pct=75"
      create=true
      key_sz=24
      value_sz=900
      icount=30000000
      report_interval=5
      run_time=1200
      populate_threads=1
      threads=((count=1,reads=1,throttle=5000))
      

      Since the workload is read-only it's possible to rerun with create=false above, and not re-create the database between runs.

      Investigating stats towards the end of such a run I see:

      WT_TEST/WiredTigerStat.04.14:Dec 04 14:11:10 2728133 WT_TEST cache: internal pages evicted
      

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              Unassigned Unassigned
              alexander.gorrod@mongodb.com Alexander Gorrod
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