[SERVER-19932] Consider increasing wiredTiger cache size default Created: 13/Aug/15  Updated: 13/Aug/15  Resolved: 13/Aug/15

Status: Closed
Project: Core Server
Component/s: WiredTiger
Affects Version/s: None
Fix Version/s: None

Type: Improvement Priority: Major - P3
Reporter: Ben McCann Assignee: Unassigned
Resolution: Duplicate Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Duplicate
duplicates SERVER-19135 Tune default cache size settings for ... Closed
Participants:

 Description   

storage:
   wiredTiger:
      engineConfig:
         cacheSizeGB: <number>

WT cache uses the higher value of 50% of system memory or 1GB by default

From what we've seen, MongoDB really needs the cache, but doesn't need much memory beyond that. We just increased to 85% of system memory and are getting dramatically better performance. Of course this may vary substantially by workload and user. However, I'd suggest that a higher default might be more appropriate for most users.

It'd be interesting to see how much heap we're using to help inform this decision, but unfortunately db.serverStatus().extra_info.heap_usage_bytes is returning a negative number - SERVER-19931



 Comments   
Comment by Ramon Fernandez Marina [ 13/Aug/15 ]

chengas123, our investigations led to a 60% default as described in SERVER-19135. Further increases may be considered in the future if thorough field testing shows it's "a good thing" for most deployments. Thus I'm going to close this ticket as a duplicate of SERVER-19135.

Regards,
Ramón.

Comment by Bruce Lucas (Inactive) [ 13/Aug/15 ]

Regarding your question about heap usage - you can get more detailed heap statistics by using db.serverStatus(

{tcmalloc:true}

). Often virtual memory will be a reasonable indication of heap usage, although there are users of memory outside of heap, for example thread stacks, which could be a substantial amount of memory if you have a lot of connections.

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