The N + 1 queries problem is a common issue Rails applications face whereby iterating an array of models and accessing an association results in a sub-optimal pattern of recurring queries. To addr...
Visualizing a Replica Set's Sync Source Chain
A MongoDB replica set is a group of mongod processes that maintain the same data set. The PRIMARY node receives all write operations and The SECONDARY nodes replicate the PRIMARY’s oplog and apply ...
MongoDB 5.0 Initial Sync Progress Monitoring Improvements
<SHAMELESS_PLUG> My previous article about initial sync progress monitoring got some attention, and as I’m a Technical Services Engineer at MongoDB, I got to provide direct feedback during t...
MongoDB 4.4 Change Streams and Experimental Pre-Image 'Support'
As of MongoDB 6.0, Change Streams Support Pre- and Post-Image Retrieval, DDL operations, and more! Warning - Not for Production Use MongoDB’s source code is available (through an SSPL license)...
Working around MongoDB Stitch's "max async work queue" limit
MongoDB Stitch is a great way to build apps quickly with your data that’s already managed by MongoDB Atlas. Though these services empower you to focus on development without having to worry about i...
Identifying and Reclaiming Disk Space in MongoDB
A common question when it comes to MongoDB and the (default) storage engine (WiredTiger) is “Why is it after I removed a bunch of documents my free space didn’t increase”? The WiredTiger storage e...
MongoDB Initial Sync Progress Monitoring
Sometimes our replica set members fall off the oplog and the node needs to be resynced. When this happens, an Initial Sync is required, which does the following: Clones all databases except the...
What is MongoDB FTDC (aka. diagnostic.data)
Full Time Diagnostic Data Capture (FTDC) was introduced in MongoDB 3.2 (via SERVER-19585), to incrementally collect the results of certain diagnostic commands to assist MongoDB support with trouble...
Troubleshooting and Fixing Invariant Failure !_featureTracker on MongoDB Startup
I recently found myself troubleshooting another MongoDB startup issue due to potential corruption within a WiredTiger file. As I have previously covered this topic (see “Recovering a WiredTiger col...
Current Date Math in MongoDB Aggregations
A challenge that I’ve had in the past while working with my data in MongoDB has been how to incorporate date math into my aggregations. db.foo.insertMany([ { lastUpdated: new Date(new Date().setDa...