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  1. Core Server
  2. SERVER-28361

Low cache usage on server

    • Type: Icon: Bug Bug
    • Resolution: Incomplete
    • Priority: Icon: Major - P3 Major - P3
    • None
    • Affects Version/s: None
    • Component/s: WiredTiger
    • None
    • ALL

      I have a 32 GB WT server running 3.0.8

      The "bytes in cache" always seem to hover around ~1GB even though I have configured the cache size to be around ~26GB.

      The total data size is around 40GB. Why is the rest of the cache not being used?

      > db.serverStatus().wiredTiger.cache
      {
      	"tracked dirty bytes in the cache" : 0,
      	"tracked bytes belonging to internal pages in the cache" : 27634342,
      	"bytes currently in the cache" : 950556531,
      	"tracked bytes belonging to leaf pages in the cache" : 27889653082,
      	"maximum bytes configured" : 27917287424,
      	"tracked bytes belonging to overflow pages in the cache" : 0,
      	"bytes read into cache" : 17875008775,
      	"bytes written from cache" : 120063944822,
      	"pages evicted by application threads" : 0,
      	"checkpoint blocked page eviction" : 4,
      	"unmodified pages evicted" : 0,
      	"page split during eviction deepened the tree" : 1,
      	"modified pages evicted" : 90924,
      	"pages selected for eviction unable to be evicted" : 20,
      	"pages evicted because they exceeded the in-memory maximum" : 1289,
      	"pages evicted because they had chains of deleted items" : 14418,
      	"failed eviction of pages that exceeded the in-memory maximum" : 15,
      	"hazard pointer blocked page eviction" : 6,
      	"internal pages evicted" : 0,
      	"maximum page size at eviction" : 10499573,
      	"eviction server candidate queue empty when topping up" : 1241,
      	"eviction server candidate queue not empty when topping up" : 3,
      	"eviction server evicting pages" : 0,
      	"eviction server populating queue, but not evicting pages" : 1243,
      	"eviction server unable to reach eviction goal" : 0,
      	"pages split during eviction" : 1374,
      	"pages walked for eviction" : 55451388,
      	"eviction worker thread evicting pages" : 2086,
      	"in-memory page splits" : 1238,
      	"percentage overhead" : 8,
      	"tracked dirty pages in the cache" : 0,
      	"pages currently held in the cache" : 16807,
      	"pages read into cache" : 2583552,
      	"pages written from cache" : 7389684
      }
      

      The only thing special about this server is that it has a large number of dbs, around 4k. Each db has around 3 collections.

            Assignee:
            mark.agarunov Mark Agarunov
            Reporter:
            dharshanr@scalegrid.net Dharshan Rangegowda
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              Created:
              Updated:
              Resolved: