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Storage-viz: Storage Visualizers and Commands for MongoDB

Nov 20 • Posted 1 year ago

Storage-viz is a suite of web-based visualizers and new experimental database commands that may help you understand how MongoDB utilizes storage and organizes btrees. Storage-viz is now available in the MongoDB Nightly builds.


When a MongoDB collection is created, an on-disk extent is allocated to store the documents. Each time a newly created or updated document cannot fit into the existing collection’s extents, a new extent is created. Each document occupies a contiguous storage area - a record - in one of the collection’s extents. Storage-viz’ experimental storageDetails command extracts information about how the disk storage is used and the web-based visualizer generates an easy-to-read graphical representation. Storage-viz also showcases which parts of the collection’s extents are currently in RAM [NOTE: the visualizer doesn’t display how much memory is available].

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How MongoDB’s Journaling Works

Oct 16 • Posted 2 years ago

This was originally posted to Kristina Chodorow’s blog, Snail in a Turtleneck

I was working on a section on the gooey innards of journaling for The Definitive Guide, but then I realized it’s an implementation detail that most people won’t care about. However, I had all of these nice diagrams just laying around.


 Good idea, Patrick! So, how does journaling work? Your disk has your data files and your journal files, which we’ll represent like this:



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