M202 July 2014 Final weeks

The first few videos of week 7 covered the write concern and some important changes to the basic parts of the system since version 2.4. It is good these subjects are explicitly covered, because MongoDB is going through a lot of functional upgrades. Without the emphasis, you might not realize there is now a more elegant way to do things.

My personal opinion is that write concern should hold no mystery this late in the course. As the other parts, it’s information you could find in the release notes.

Snapshot of operations

The next topic of the videos was interesting, but could have had more depth to it. A video was spent on the database command currentOp which will spew data on the operations of the current mongod process. This command generates a lot of data, but the important thing to remember is and most importantly is a snapshot in time. The videos went over some basic scenarios on how to use the database command and the reliability of the information.

This is all nice, until your system has a heavy load and capturing that problem becomes too difficult for a (wo)man and a simple shell. That’s when you need tools that are able to capture and process faster then most humans can do.


During the course there were some videos on mtools. If you wouldn’t know it’s related to MongoDB then you stumble onto several other software tools and packages with that name. This gets confusing when you search your favorite package manager, you will probably not find the tool you’re looking for.

The mtools mentioned in this course are a collection tools written in Python to simplify several tasks when experimenting with MongoDB or analyzing its output. This software isn’t officially supported by MongoDB Inc., but was written by a current employee and found it’s way across his peers.

The source and installation can be found on GitHub. You might have some trouble setting up the software correctly, because sometimes library dependencies not enforced to a particular version or need to be forcefully updated. This can be very frustrating and give the idea the tools don’t work, where installation of all the right versions of dependencies will make it work as intended.

So what can mtools do? It can set up basic architectures of MongoDB systems. For instance, it’s interface to setting up a sharded cluster is quite nice. The course material demonstrated it and I prefer the mtools way to the mongo shell’s ShardingTest object. Both mtools and the mongo shell can only start processes on the local system, which is good enough for experiments.

It can also filter, combine and plot log data. There are a lot of tools that can do that, but mtools doesn’t need tweaking to understand MongoDB’s log format and comes with some default reports that make sense. That being said, there are definitely tools that have a sleeker appearance, create more attractive reports or just integrate better with other tools.

If I would be faced with an immediate problem in a MongoDB cluster, then churning through the logs with mtools would be my preference. MongoDB Management Service be a second choice, because it takes some time for data to show up and it’s not as detailed. In time I would be looking for other tools to specifically suit what I need as a tool.


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