Mongodb hotfix KB2731284
I installed MongoDb on a windows server 2008 R2 and the hotfix KB2731284 is not installed, but I cannot restart the server easily.
In the hotfix description, I got this message "You run an application that uses the FlushViewOfFile() function to clean up memory-mapped files from the paged memory pool." (see https://support.microsoft.com/en-us/kb/2731284)
My question is, when the funtion FlushViewOfFile() is called? My application is just writing in a collection and get data from it. Do I risk to get some wrong behaviors?
Answer
I think you can run MongoDb without applying the Hotfix, but I would not recommend it. In long time you may run into problems. They have included some fixes in MongoDB to workaround the problem.
A detailed description of the problem can be found here and here.
See also this.
On Windows, Memory Mapped File flushes are synchronous operations. When the OS Virtual Memory Manager is asked to flush a memory mapped file, it makes a synchronous write request to the file cache manager in the OS. This causes large I/O stalls on Windows systems with high Disk IO latency, while on Linux the same writes are asynchronous.
The problem becomes critical on high-latency disk drives like Azure persistent storage (10ms). This behavior results in very long bg flush times, capping disk IOPS at 100. On low latency storage (local storage and AWS) the problem is not that visible.
On Windows 7 and Windows Server 2008 R2 when applying the hotfix you get a better file allocation performance what is relevant for MongoDB