5 Immidiate Steps to Take Care of Your MongoDB Performance

Do you face some performance issues in your MongoDB setup?
In this case use the following steps to provide some first aid to your system and gain some space for a long term architecture (such as Sharding)

Step 1: Enable slow queries
Get intelligence about your system behavior and performance bottlenecks. Usually there is a high correlation between the slow queries and your performance bottleneck, so use the following method to enable your system profiling collection:
db.setProfilingLevel(1, 100);

Step 2: Use explain
Explore the problematic queries using explain. You can also use mtools to analyze the logged queries to find high frequent ones.

Step 3: Create indexes
Your analysis should result with new indexes in order to improve the queries
Don't forget to use index buildup in the background to avoid collections locking and system downtime.

Step 4: Use sparse indexes to reduce the size of the indexes
If you use sparse documents, and heavily using the $exists key words in your queries, using sparse indexes (that includes only documents that includes your field) can minimize your index size the boost your query performance.

Step 5: Use secondary preferred to offload queries to slaves
You probably have a replica set and it's waste of resources not using your slaves for read queries (especially for reporting and search operations).
By changing your connection string to secondary preferred, your application will try to run read queries on the slaves before doing that on your master.
Bottom Line
Using these simple method, you can gain time and space before hitting the wall.

Keep Performing,
Moshe Kaplan

Prepare for Failure in Your AWS Environment

In the cloud everything can happen. 
Actually everything will happen.

Therefore, in your design, you should be ready for failures: even if you expect your disk mounts to be there for you, they might not be. And you are doing auto scaling, it is most likely that one in a time they won't be there for you.

Therefore, to avoid hanging servers due to failure to mount disks and bad messages as the follow: "The disk drive for /tmp is not ready yet or not present", make sure your servers are not bound by your disks (otherwise you will not be able to contact your servers, or your OpsWorks will notify you that the server is booting forever).

Avoiding Waiting for Your Mount
The secret is a small option: nobootwait that will make sure your server is not waiting for the mount to be ready. You can configure it in your /etc/fstab, or even better in your Chef recipe:
mount "/tmp" do
  device "172.32.17.48:/tmp"
  fstype "nfs"
  options "rw,nobootwait"
  action [:mount, :enable]
end

Bottom Line
The right design will help you keep you system running in a cloud based environment

Keep Performing,
Moshe Kaplan