I’ve been doing replica set “bootcamps” for new hires. It’s mainly focused on applying this to debug replica set issues and being able to talk fluently about what’s happening, but it occurred to me that you (blog readers) might be interested in it, too. There are 8 ...
MongoDB is an open source, high-performance, schema-free, document-oriented database written in the C++ programming language. It manages collections of BSON documents that can be nested in complex hierarchies and still be easy to query and index, which allows many applications to store data in a natural way that matches their native data types and structures.
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––thursday #5: diagnosing high readahead
Having readahead set too high can slow your database to a crawl. This post discusses why that is and how you can diagnose it. The #1 sign that readahead is too high is that MongoDB isn’t using as much RAM as it should be. If you’re running Mongo ...
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Night of the Living Dead Ops
MongoDB users often ask about the “killed” field in db.currentOp() output. For example, if you’ve run db.killOp(), you might see something like: > db.currentOp() { "inprog" : [ { "opid" : 3062962, "active" : true, "lockType" : "write", "waitingForLock" : false, "secs_running" : 32267, "op" : "update", "ns" : "httpdb.servers", ...
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The Comments Conundrum
One of the most common questions we get is: I have a collection of blog posts and each post has an array of comments. How do I get… …all comments by a given author …the most recent comments …the most popular commenters? And so on. The answer to this has ...
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Hacking Chess: Data Munging
This is a supplement to the Hacking Chess with the MongoDB Pipeline. This post has instructions for rolling your own data sets from chess games. Download a collection of chess games you like. I’m using 1132 wins in less than 10 moves, but any of them should work. These ...
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Hacking Chess with the MongoDB Pipeline
MongoDB’s new aggegation framework is now available in the nightly build! This post demonstrates some of its capabilities by using it to analyze chess games. Make sure you have a the “Development Release (Unstable)” nightly running before trying out the stuff in this post. The aggregation framework will be ...
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Querying for Timestamps Using ObjectIds
ObjectIds contain a timestamp, which tells you when the document was created. Because the _id field is always indexed, that means you have a “free” index on your “created at” time (unless you have persnickety requirements for creation times, like resolutions of less than a second, synchronization across app servers ...
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SQL to MongoDB: An Updated Mapping
The aggregation pipeline code has finally been merged into the main development branch and is scheduled for release in 2.2. It lets you combine simple operations (like finding the max or min, projecting out fields, taking counts or averages) into a pipeline of operations, making a lot of things ...
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On working at 10gen
10gen is trying to hire a gazillion people, so I’m averaging two interviews a day (bleh). A lot of people have asked what it’s like to work on MongoDB, so I thought I’d write a bit about it. A Usual Day Get in around 10am. Check if ...
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Getting Started with MMS
Telling someone “You should set up monitoring” is kind of like telling someone “You should exercise 20 minutes three times a week.” Yes, you know you should, but your chair is so comfortable and you haven’t keeled over dead yet. For years*, 10gen has been planning to do monitoring ...