[SERVER-21805] RAM usage - slow down server Created: 09/Dec/15  Updated: 09/Dec/15  Resolved: 09/Dec/15

Status: Closed
Project: Core Server
Component/s: WiredTiger
Affects Version/s: 3.0.3
Fix Version/s: None

Type: Bug Priority: Major - P3
Reporter: Niti Test Assignee: Unassigned
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Attachments: Text File sm11_serverStatus.txt    
Operating System: ALL
Steps To Reproduce:

1. RS with WT
2. Collection with 500 GB data
3. Loop over the collection (we use PHP)

Participants:

 Description   

We have a replica set with one secondary and one arbiter (each on a different server) and moved from MMapv1 to WiredTiger. Primary and Secondary each have 32 GB. We have now a process where we read each document once. The mongod process uses all of the 32 GB RAM and the server is very slow.
Attached you will find our serverStatus: wt cache size is 16 GB, tcmalloc size is 26 GB.
So the question for us is, why WT uses all of the 32 GB and swaps now and how can we fix that. Also, if we upgrade to a new version, we see in the jira tasks, that there are a lot of problems with memory leaks together with WT. So what recommendation do you have.

free -m output:
total used free shared buffers cached
Mem: 32136 31727 409 0 9 2899
-/+ buffers/cache: 28819 3317
Swap: 49152 609 48543



 Comments   
Comment by Ramon Fernandez Marina [ 09/Dec/15 ]

k9908600@gmx.at, there are some known issues with excessive memory consumption in early 3.0 versions, so I'd recommend you upgrade to 3.0.7. Note that 3.2.0 was released yesterday and contains many improvements in this area, as well as new features and performance enhancements, so you may want to give 3.2.0 a try.

Both for 3.0 and 3.2 you should be aware of the WiredTiger cache size and can try lowering its value.

Please note that the SERVER project is for reporting bugs or feature suggestions for the MongoDB server. For MongoDB-related support discussion please post on the mongodb-user group or Stack Overflow with the mongodb tag, where your question will reach a larger audience. A question like this involving more discussion would be best posted on the mongodb-user group. See also our Technical Support page for additional support resources.

Regards,
Ramón.

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