[DOCS-4037] Mongod and VMware vmmemctl (balloon driver) needs an official explanation Created: 12/Sep/14  Updated: 30/Oct/23  Resolved: 03/Apr/15

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

Type: Task Priority: Major - P3
Reporter: Ricardo Lorenzo Assignee: Michael Paik
Resolution: Done Votes: 0
Labels: hypervisor, vmware
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Participants:
Days since reply: 7 years, 29 weeks ago

 Description   

The balloon driver for VMWare (or Xen, Hyper-V,etc) seems like is not compatible with mongod.

The explanation about the balloon driver utility is the following:

If a database VM needs to compete for the same physical memory space with other VMs, the hypervisor could start allocating memory on disk.

Using vmmemctl (balloon driver), if the hypervisor decides that it wants to reduce the amount of physical memory used by the VM, the driver starts to perform memory allocations inside the VM pushing out other memory data to disk (to the swap space).

This behaviour is highly desirable in general, because otherwise the hypervisor would have to allocate the VM memory data in it's own swap file. In that case the OS believes that it has allocated physical memory, and the application will experience some unexplainable delays and result in performance problems.

The main concern with the balloon driver relates to the experience of some of our customers in which crashes no longer occur when the driver is disabled.

I found a bug in the driver related to mmap allocation. IMHO VMware bug KB1003586 do not affect mongod because it don't pin or lock memory pages (SERVER-8121) for now.

Our recommendation is to disable the balloon driver, but I might add the need for reserve sufficient physical memory in the hypervisor for the VM to ensure the database’s working set fits within it.



 Comments   
Comment by Emily Hall [ 27/Jul/16 ]

Closed for housekeeping on 7/27/2016 by Emily Hall.
If you require additional support, please open a new ticket for prioritization.
Thanks,
Emily

Comment by Githook User [ 03/Apr/15 ]

Author:

{u'username': u'mpaik', u'name': u'Michael Paik', u'email': u'michael.paik@10gen.com'}

Message: DOCS-4037
Branch: master
https://github.com/mongodb/docs/commit/f137430b479fc6f765575c595f32f7ff8aaf141c

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