[DOCS-9228] 3.0 Wired Tiger cache utilization documentation needs to say it rounds down to the closest whole integer value of GB Created: 28/Oct/16  Updated: 30/Oct/23

Status: Closed
Project: Documentation
Component/s: manual, Server
Affects Version/s: None
Fix Version/s: Server_Docs_20231030

Type: Improvement Priority: Major - P3
Reporter: Shakir Sadikali Assignee: Kay Kim (Inactive)
Resolution: Won't Do Votes: 0
Labels: bite-sized
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Participants:
Days since reply: 1 year, 14 weeks, 2 days ago
Epic Link: DOCSP-1769
Story Points: 0.25

 Description   

I have confirmed the behavior with the Wired Tiger development team. By default, the Wired Tiger cache will be set to a rounded down whole integer value GB. In your system, we see that the memory configured is

```
MemTotal: 8057784 kB
```

50% of this is 4028892 KB =~ 3.8GB. This gets rounded down to 3GB.

See the following:

```
> db.adminCommand(

{ "setParameter": 1, "wiredTigerEngineRuntimeConfig": "cache_size=3.7G"}

)

{ "was" : "", "code" : 2, "ok" : 0, "errmsg" : "WiredTiger reconfiguration failed with error code (22): Invalid argument" }

```

This shows that the parameter needs to be a whole integer value.

```
> db.adminCommand(

{ "setParameter": 1, "wiredTigerEngineRuntimeConfig": "cache_size=4G"}

)

{ "was" : "", "ok" : 1 }

```

We should clarify that we aren't actually using 50% in 3.0.



 Comments   
Comment by Education Bot [ 31/Oct/22 ]

Hello! This ticket has been closed due to inactivity. If you believe this ticket is still important, please reopen it and leave a comment to explain why. Thank you!

Comment by Kelsey Schubert [ 28/Oct/16 ]

In MongoDB 3.4, WiredTiger cache size will not be rounded down, see SERVER-23624.

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