Mastering MongoDB 4.x - Second Edition

Snapshots and checkpoints

WiredTiger uses Multi-Version Concurrency Control (MVCC). MVCC is based upon the concept that the database keeps multiple versions of an object so that readers will be able to view consistent data that doesn't change during a read.

In a database, if we have multiple readers accessing data at the same time that writers are modifying the data, we can end up with a case where readers view an inconsistent view of this data. The simplest and easiest way to solve this problem is to block all readers until the writers are done modifying data.

This will, of course, cause severe performance degradation. MVCC solves this problem by providing a snapshot of the database for each reader. When the read starts, each reader is guaranteed ...