Question

I am concern about my server machine performance . The application deals with gazillion data from RETS sever feed. Whenever server starts mongod service its getting like taking off the performance and the PF usage shoot upto ~3.59GB although it has good configuration(Server2008, 4GB RAM) and using mongodb 64bit latest release (2.0.6).Please enlighten me on this regard.

Thanks

Answer 1

I’m not sure how much you know about MongoDB but Mongo uses memory mapped files to access data, which results in large numbers being displayed for the mongod process. This is normal when using memory-mapped files. The amount of mapped datafile is shown in the virtual size parameter and resident bytes shows how much data is being cached in RAM. The larger your data files, the higher the vmsize of the mongod process.

If other processes need more ram, the operating system’s virtual memory manager will relinquish some memory from the cache and the resident bytes on mongod process will drop.

It is recommended to use a fixed pagefile size. If you use a dynamic page file the OS doesn’t increase it fast enough to keep up with the (private) mapped memory calls. There’s actually an open ticket to add special warning if the page file is dynamic or (min is) set too small.

This document explains how memory usage works on MongoDB.

Here are some tools that show how you can diagnose system issues with MongoDB –

• mongostat
• Monitoring and Diagnostics

To be honest, I’d recommend moving this issue to the MongoDB User Google Group and posting your issue there along with the mongostat output during the issue as well as information from perfmon as this will likely be a longer discussion.