These are some sparse notes I took at a free MongoDB presentation I attended at Urban Rethink in Downtown Orlando, FL. The event was called An Evening with MongoDB

Features of MongoDB

• BSON is nomal JSON but with typed data
• Ad-hoc query support - secondary index
• effective for an array of value or  set search
• has a ttl collection that expires data
• various indexes - 2d, sparse ....
• geospacial indexes - like with zillow
• lacks
  • joins,
  • multi-collection transactions (2 face commit)
  • no transactions but uses document level locks
• search for mongodb cookbook

Replication

• arbitratry node prevents 2 nodes from gaining master status if the master failes
• recommends 3 nodes
• getLastError will not loose data sent to a failing master and will retry on the new masters
• mostly checked on the application side
• can check the health of a node

Sharding

• horizontal scaling
• no application logic needed
• range based partition mechanism
• shard key - can be composite keys ( ie username/date)
• geospacial sharding in future releases
• replacing a shard will slow down application as it rebuilds
• driver connects to mongoS that takes care of sharding

Mongo 2.2

• concurrency improvements
  • db level locking
  • improved yielding
• ttl will delete data after a certain amount of time (like session data). sometime after the time and can be backed up. minute interval.
• Ask for a soft delete feature with the ttl - it currently only deletes it
• Can normalize data using a pson function. No triggers yet. application has to check data being inserted
• JIRA ticketing system for bugs, requests...

 

 

Aggregation Framework

• MapReduce - scans collections and finds data you're looking for. Groups and sorts it. Then reduces and outputs it to a collection to analyze it.
  • Overkill for simple aggregation tasks
  • Implementd with js
  • single threaded
  • difficult to debug
  • concurrency
    • appearance of parralllism

Aggregation Functions

• $project
• $match
• • match in pipeline
• $group
• • group during aggregation
  • group by constant id to group on the entire collection
  • array of set operators
  • addtoset takes out duplicates, push doesn't
  • $unwind
  • • operates on an array field and then you can group on it
• $sort
• • has to wait for all operators to finish
• $limit
• $skip

extending framework can add new pipeline operators and expressions

$out and $tee for output and debugging

 

early filtering

• match
• sort
• limiy
• group
• sort
• project

operation memory limits
$group and $sort entirely in memory. warning > 5% and errors >5%
returns results, but returns an error code

 

sharding - splits the pipeline at first group or sort

 

github.com/rozza/demos

 

OpenShift

Titanium studio

• can port code to different languages from js
• ideal for mongo because it uses js
• application as a service

github.com/beershift