Memory and storage engine basics (WiredTiger) in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the WiredTiger storage engine in MongoDB?

WiredTiger is the default storage engine in MongoDB that manages how data is stored on disk and cached in memory. It uses compression and supports document-level concurrency control for better performance.

beginner

How does WiredTiger use memory for caching?

WiredTiger uses a cache in RAM to store frequently accessed data and indexes. This cache speeds up read and write operations by reducing disk access.

intermediate

What is document-level locking in WiredTiger?

Document-level locking means WiredTiger locks only the specific document being changed, not the whole collection. This allows many operations to happen at the same time without waiting.

intermediate

Why does WiredTiger use compression for data storage?

WiredTiger compresses data to save disk space and reduce the amount of data read from or written to disk, which improves speed and efficiency.

advanced

What happens if the WiredTiger cache is full?

When the cache is full, WiredTiger writes dirty data (changes) to disk to free up space. This process is called checkpointing and helps keep data safe and memory available.

What is the default storage engine in MongoDB?

A RocksDB

B MMAPv1

C InMemory

D WiredTiger

WiredTiger is the default storage engine in MongoDB since version 3.2.

What type of locking does WiredTiger use to improve concurrency?

A Document-level locking

B Database-level locking

C Collection-level locking

D No locking

WiredTiger uses document-level locking to allow multiple operations on different documents simultaneously.

Why does WiredTiger use compression?

A To reduce disk space and improve speed

B To increase disk space usage

C To slow down data access

D To encrypt data

Compression reduces disk space usage and speeds up data access by reading and writing less data.

What does WiredTiger do when its cache is full?

A Deletes old data

B Writes dirty data to disk (checkpointing)

C Stops accepting writes

D Increases cache size automatically

WiredTiger writes dirty data to disk to free cache space, a process called checkpointing.

What is stored in the WiredTiger cache?

A Only indexes

B Only data

C Frequently accessed data and indexes

D Backup files

The cache holds frequently accessed data and indexes to speed up operations.

Explain how WiredTiger manages memory and storage to improve MongoDB performance.

Think about caching, locking, compression, and writing data safely.

Describe the benefits of document-level locking in WiredTiger.

Compare locking at document level vs collection level.