MongoDB for Developers with Python Transcripts
Chapter: What is NoSQL?
Lecture: Types of NoSQL databases

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0:01 So this historical description indicates that there are
0:03 a variety of different types of NoSQL databases that we've arrived at,
0:07 basically different levels or types of trade-offs that you might make
0:11 to encourage this horizontal scalable, cluster friendly type of data.
0:15 Now, if you go and look this up, what are the types of NoSQL systems
0:18 you'll see there are four distinct types,
0:21 but I think that would be four types under the not only SQL style systems
0:26 which as that my contention, that's not what NoSQL is.
0:30 So, I think there's actually three types of NoSQL databases
0:33 and then there's another thing that is not SQL; we'll talk about the four.
0:37 So at the most basic, basic level, the simplest ones are
0:41 I'm going to basically create a distributed dictionary
0:44 with id key that I can look up and some opaque blob that I can get back
0:49 so here is some thing, it could be text, it could be binary object, graph,
0:54 it doesn't really matter, store to this key
0:57 and if I ask for that key back give me the thing,
0:59 so for example, I want to store a user and all the stuff
1:03 that is associated with user into a single blob in Redis,
1:06 and when I ask for it back by user id, giving that thing back.
1:11 That means frequently these databases, these key value stores
1:14 don't let you query inside the opaque blob, even if it's text,
1:18 the idea is you query by the id, you get the thing,
1:21 but you can't easily ask it questions like
1:25 what is the average price of the order
1:28 of all the customers stored in your key value store.
1:31 Now, there are ways to add like additional metadata
1:34 that you can stick on to them, so you can sort of fake it a little bit on some of them
1:38 but in general, I can ask for the thing by a key
1:42 and I get a blob that's opaque to the database back.
1:45 Now, these are not great as databases in terms of general purpose databases
1:49 because you can't ask them a wide variety of interesting questions.
1:53 However, they are great in terms of this cluster ability
1:56 of the distributed cash type of thing there is super, super fast,
2:01 because every single query is just finally one item
2:04 by primary key and get it back to me
2:08 so if you horizontally scale that out, you can find
2:10 which key range maps to which server,
2:12 go to that server get it by id— boom, super, super fast.
2:15 So these are nice, they are often used for caches and things like this.
2:19 Next, we have what I think is the real sweet spot for NoSQL databases,
2:25 the ones that potentially could replace
2:27 traditional relational databases in your application,
2:30 that is they are flexible and powerful enough to be general purpose databases
2:35 and that's the document databases.
2:37 So this is MongoDB, CouchDB, OrientDB,
2:40 DocumentDB from Microsoft Azure, things like that,
2:43 so this is really where we going to focus
2:46 almost this entire class, so we'll come back to this.
2:49 We also have a more interesting type of database
2:52 called a columnar database, traditional relational database systems
2:56 like MySQL, Microsoft SQL server etc, store data in rows,
3:01 but a column oriented database is different
3:04 in that it stores data and its tables as columns instead of rows;
3:07 so it's in a lot of ways really similar to relational databases,
3:11 but you'll find that it's easier to kind of associate
3:14 what you might think of is like a pre-joint data,
3:16 maybe some orders, and maybe the orders have order items
3:19 and there's a bunch of those, so you might have one order
3:22 with multiple items, it's easier to group those together in a columnar database.
3:26 But they're kind of more or less like relational databases in a lot of ways.
3:30 So these I believe are the three types of NoSQL databases.
3:32 There's a fourth that often gets grouped here,
3:35 so let's talk about it— graph databases.
3:37 So graph databases let you model relationships
3:40 on many, many small interconnected things
3:44 so think of like social graphs, friends, the pictures,
3:48 the people who have shared that picture, you've liked that picture,
3:52 the friends of your friends who have liked that particular picture
3:55 you can traverse these relationships incredibly easy in graph databases
3:59 because you can actually query directly on the relationships.
4:03 Show all the things related in this way to this item and so on,
4:06 but that does not lead to this cluster friendly sort of thing,
4:09 in fact, this leads to being even more tightly connected
4:12 the less easy to map across multiple
4:15 horizontally scaled servers and things like that.
4:18 So in my mind, the graph databases are super interesting
4:21 but they're not NoSQL they're just not-SQL.
4:25 So that leaves us with three types—
4:27 key value stores, document databases and columnar databases.
4:30 So let's now continue on to talk about document databases.