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What is MongoDB WiredTiger?
WiredTiger is a NoSQL, Open Source extensible platform for data management. The WiredTiger storage engine is the default storage engine starting in MongoDB version 3.2. It provides a document-level concurrency model, checkpointing, and compression, among other features.
Does MongoDB store data in memory or disk?
MongoDB is not an in-memory database. Although it can be configured to run that way. But it makes liberal use of cache, meaning data records kept memory for fast retrieval, as opposed to on disk. There is much bad information on StackOverflow about what to do when your server runs out of memory.
How is data represented in WiredTiger internal cache?
Different representations are used for data in the WiredTiger internal cache versus the on-disk format: Data in the filesystem cache is the same as the on-disk format, including benefits of any compression for data files. The filesystem cache is used by the operating system to reduce disk I/O.
How big is the WiredTiger cache in MongoDB?
Starting in MongoDB 3.4, the default WiredTiger internal cache size is the larger of either: 50% of (RAM – 1 GB), or 256 MB. For example, on a system with a total of 4GB of RAM the WiredTiger cache will use 1.5GB of RAM (0.5 * (4 GB – 1 GB) = 1.5 GB).
How does WiredTiger storage engine improve low latency?
Extensive usage of cache rather than disk to enhance low latency. WiredTiger storage engine relies heavily on the OS page-cache such that compressed data is fetched without involving the disk. Besides, the least recently used data is cleared from the RAM preserving more space for the cache.
What kind of storage engine does WiredTiger use?
The storage engines are: The WiredTiger storage engine has both configurations of a B-Tree Based Engine and a Log Structured Merge Tree Based Engine. This is one of the ancient storage engines from which other sophisticated setups are derived from.