Istanbul HackersGeekly Weekly

Mongo DB@hserdarb

Why MongoDB?

• Easy to use nosql

• Good for web projects

• Popular

• High performance (No joins and embedding makes reads and writes fast)

• High availability (Replicated servers with automatic master failover)

• Easy scalability (Automatic sharding)

What’s MongoDB good for?

• Account and user profiles: can store arrays of addresses with ease

• CMS: the flexible schema of MongoDB is great for heterogeneous collections of content types

• Form data: MongoDB makes it easy to evolve structure of form data over time

• Blogs / user-generated content: can keep data with complex relationships together in one object

• Messaging: vary message meta-data easily per message or message type without needing to maintain separate collections or schemas

• System configuration: just a nice object graph of configuration values, which is very natural in MongoDB

• Log data of any kind: structured log data is the future

• Graphs: just objects and pointers – a perfect fit

• Location based data: MongoDB understands geo-spatial coordinates and natively supports geo-spatial indexing

http://blog.mongolab.com/2012/08/why-is-mongodb-wildly-popular/

The Modern Need From Databases

• Easy to use when project is small

• Developing schema less

• When we need scale it must be easy and cheap

• No data loss

• High Availability

RDBMS => MongoDB

RDBMS MongoDB

Table, View Collection

Row JSON Document

Index Index

Join Embeded Document

Partition Shard

Partition Key Shard Key

What is BSON?

• MongoDB uses BSON as the data storage and network transfer format for "documents".

• Short for Binary JSON

• http://bsonspec.org/

• http://www.mongodb.org/display/DOCS/BSON

Working with Entity Objects

• Things can be really easy for you if you follow these rules for yourentities• Has a public no-argument constructor

• Has a public get set property for each value you want to have serialized

CRUD

https://github.com/serdarb/IstanbulHackersCodeReviewSample/blob/master/AgileWall.Domain/Repo/BaseRepo.cs

Write Concern

• Acknowledged• Write operations that use this write concern will wait for acknowledgement from the primary

server before returning.

• Unacknowledged• Write operations that use this write concern will return as soon as the message is written to

the socket.

• Journaled• Exceptions are raised for network issues, and server errors; the write operation waits for the

server to group commit to the journal file on disk.

• Replica Acknowledged• Exceptions are raised for network issues, and server errors; waits for at least 2 servers for the

write operation.

http://docs.mongodb.org/manual/core/write-concern/http://api.mongodb.org/java/current/com/mongodb/WriteConcern.html

https://github.com/mongodb/mongo-csharp-driver/blob/master/MongoDB.Driver/WriteConcern.cs

Journaling

• Process starts with private view

• Private view writes to journal

• Journal updates shared view

• Shared view updates private view

• Shared view flushes data to disk

http://www.kchodorow.com/blog/2012/10/04/how-mongodbs-journaling-works/

Index

• BasketItems.CreateIndex(“UserId”);

A tip for better indexing

• Run mongodb with notablescan parameter and be sure your your queries are not making full table scans...• You get exceptions if a query needs a table scan, it gives you a chance to fix

your indexes on development time.

Map Reduce

Transaction

• MongoDB does not support transactions.

• It is good to use relational databases (oracle, sql server) for this purpose

• If you are stuck in a situation that needs transactions with MongoDB you must implement it by your self.• http://docs.mongodb.org/manual/tutorial/perform-two-phase-commits/

• https://github.com/rystsov/mongodb-transaction-example

Sharding & ReplicationSharding is for scale out, replication is for high availability

Replication

• Copies of your data for data safety

• Asynchronous replication

• Master - Slave model• Not master-master, when your data change

there are times that you only have one master…

• Statement based• For example, insert statement send to the

replica and will run there…

• Driver is replica set aware,

• Connection to replica set mongodb://server1,server2:27017,server2:27018

Sharding (partitioning)

• MongoDB does range based partitioning• Name begins with A, B-E, F-H ….

• Shardkey is important!• Bad shard key choice can cause

too many split and merge operations on chunks

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Sources

• education.10gen.com• http://openmymind.net/mongodb.pdf• http://www.mongodb.org/display/DOCS/Introduction

• http://www.mongodb.org/display/DOCS/Padding+Factor

• https://github.com/mongodb/mongo

• http://www.codeproject.com/Articles/273145/Using-MongoDB-with-the-Official-Csharp-Driver

• http://stackoverflow.com/questions/4067197/mongodb-and-joins

• http://www.mongodb.org/display/DOCS/Schema+Design#SchemaDesign-EmbeddingandLinking

• http://docs.mongodb.org/manual/applications/database-references/

• http://www.10gen.com/presentations?programming_lang=46

• https://speakerdeck.com/mongodb/whats-new-in-the-net-driver

• http://learnmongo.com/

• http://www.mongovue.com/2010/11/03/yet-another-mongodb-map-reduce-tutorial/

• http://spp42.com/mongodbde-dogru-index-kullanimi-nasil-kontrol-edilir-i/

• http://bjclark.me/2009/08/nosql-if-only-it-was-that-easy/

• http://reactivemongo.org/