[SERVER-6528] mongod pmap contain db files not in one copy Created: 19/Jul/12  Updated: 15/Aug/12  Resolved: 20/Jul/12

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

Type: Question Priority: Major - P3
Reporter: Azat Khuzhin Assignee: Unassigned
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Attachments: File mongod-pmap-db-files-not-in-one-copy    
Participants:

 Comments   
Comment by Azat Khuzhin [ 20/Jul/12 ]

Thanks for the explanation

Comment by Andy Schwerin [ 20/Jul/12 ]

It does not increase the physical memory consumption. The private view and shared view are nearly the same, except that the private view contains writes that have not yet been retired out of the journal. Up to 100MB worth of data in the two views are allowed to be distinct, but this could be thought of as space to buffer uncommitted writes.

The virtual address space consumption is a little under double the physical memory consumption, for this reason. On 64-bit x86 systems available today, this would limit a single mongod to storing around 64TB worth of data, even though there are 128TB of virtual address space available to a process.

Comment by Azat Khuzhin [ 20/Jul/12 ]

Does this increase the memory usage?
For what mongod may need and MAP_PRIVATE and MAP_SHARED ?

Comment by Eliot Horowitz (Inactive) [ 20/Jul/12 ]

This is normal.
There is a for the private view, and 1 for the shared.

Comment by Azat Khuzhin [ 19/Jul/12 ]

Is it normal and why it is possible?
Thanks.

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