MongoDB

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MongoDB

MongoDB is a general purpose, document-based, distributed database built for modern application developers and for the cloud era.

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Learn

Official resources

: presentations, webinars, white papers

Key features

Flexible schema
Performance
High Availability
- Primary / Secondaries architecture
BSON storage (Binary JSON)
- support of for encoding a variety of geographic data structures
ACID transactions
Sharding

Replication

A replica set is a group of mongod processes that maintain the same data set. Replica sets provide redundancy and high availability.

A node of the replica set can be: Primary, Secondary, Arbitrer.

Read preference

Write concern

Read concern

Indexing

Indexes gets have better read time but have an impact on write time.

Index Types:

Single Field
Compound Index
Multikey Index
Geospatial Index
Text Indexes
Hashed Indexes

Index Properties:

Unique Indexes
Partial Indexes
Sparse Indexes
TTL Indexes (Time To Live)

Performance

Storage engine

The storage engine that is used can be seen with the command db.serverStatus(). It is a mongod option: --storageEngine.

In March 2015, there were two choices: MMAPv1 (original) and WiredTiger (new).

Wired Tiger is new in MongoDB 3.0. It is the first pluggable storage engine.

Features:

Document level locking
Compression
- Snappy (default) - fast
- Zlib - more compression
- None
Lacks some pitfalls of MMAPv1
Performance gains

Background:

Built separately from MongoDB
Used by other's DB
Open source

Internals:

Stores data in btrees
Writes are initially separate, incorporated later
Two caches
- WT caches - 1/2 of RAM (default)
- FS cache
Checkpoint: every minute or more
No need for a journal

Transactions

High availability

Data types

Products

Getting further

Recipes

Releases

Version

Date

4.4

June 09, 2020

First steps

MongoDB Shell

MongoDB Shell on Windows

You'll download a file like mongodb-win32-x86_64-2008plus-ssl-4.0.4.zip
Unzip the content of the archive in a program folder (for example D:\Programs folder)
Rename the folder with something explicit like mongodb-community-4.0.4
You can either update your PATH globally on your machine or do it when you need it (or through a bat file)
```
SET PATH=%PATH%;D:\Programs\mongodb-community-4.0.4\bin
```

First commands

The following command must return a valid output
```
mongo --version
```
MongoDB shell version v4.0.4 git version: f288a3bdf201007f3693c58e140056adf8b04839 allocator: tcmalloc modules: none build environment: distmod: 2008plus-ssl distarch: x86_64 target_arch: x86_64

Local Server

If you followed the steps to have the Mongo Shell, you'll be able to launch easily a MongoDB server locally (mongod).

# make sure the data path exists
md /path/to/data
# start a basic MongoDB instance (default port 27017)
mongod --dbpath=/path/to/data

You can then connect with the MongoDB Shell:
```
mongo
```

Docker

Check the images already downloaded locally
```
docker images
```
Get the image for a specific version of MongoDB
```
docker image pull mongo:4.0.4
```

Start the container

docker run -d -p 27017:27017 --name mongodb404 mongo:4.0.4

Server

Start with Docker

docker run --name mongodb -d -p 27017:27017 mongo:4.4.6

Start from the command line

mongod --dbpath "C:\my\path" --port 27017

Client

Command line

# start a mongo shell and be on mycollection
mongo --port 27017 mycollection

# restore from dump folder into mydbname database
mongorestore -d mydbname dump

# monitor basic usage statistics for each collection
mongotop

# monitor basic MongoDB server statistics
mongostat

MongoDB Shell (mongosh)

Introduced in June 2020, avalable as a standalone package, it provides a fully functional JavaScript/Node.js environment for interacting with MongoDB deployments. It can be used to test queries and operations directly with one database.

mongosh <connection_string>

Sample data

Zip code

Import the data into your MongoDB server

# to be run in the folder containing the json file
mongoimport --db demoZip --collection zips --file zips.json
# it should generate the following output
# 2018-11-19T14:48:53.296+0100    connected to: localhost
# 2018-11-19T14:48:53.705+0100    imported 29353 documents

You can also import the data to your Atlas cluster

mongoimport --uri "mongodb+srv://user:password@mycluster.mongodb.net/demoZip" --collection zips --file zips.json

dbKoda samples

Open source tools

mtools

mtools is a collection of helper scripts to parse, filter, and visualize MongoDB log files (mongod, mongos). mtools also includes mlaunch, a utility to quickly set up complex MongoDB test environments on a local machine.

You'll need Python (2 or 3) to install and use it.

# install with pip (Python)
pip install mtools

Deployment typologies

MongoDB & OVH

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Last updated 1 year ago

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