00:01 So this historical description indicates that there are
00:03 a variety of different types of NoSQL databases that we've arrived at,
00:07 basically different levels or types of trade-offs that you might make
00:11 to encourage this horizontal scalable, cluster friendly type of data.
00:15 Now, if you go and look this up, what are the types of NoSQL systems
00:18 you'll see there are four distinct types,
00:21 but I think that would be four types under the not only SQL style systems
00:26 which as that my contention, that's not what NoSQL is.
00:30 So, I think there's actually three types of NoSQL databases
00:33 and then there's another thing that is not SQL; we'll talk about the four.
00:37 So at the most basic, basic level, the simplest ones are
00:41 I'm going to basically create a distributed dictionary
00:44 with id key that I can look up and some opaque blob that I can get back
00:49 so here is some thing, it could be text, it could be binary object, graph,
00:54 it doesn't really matter, store to this key
00:57 and if I ask for that key back give me the thing,
00:59 so for example, I want to store a user and all the stuff
01:03 that is associated with user into a single blob in Redis,
01:06 and when I ask for it back by user id, giving that thing back.
01:11 That means frequently these databases, these key value stores
01:14 don't let you query inside the opaque blob, even if it's text,
01:18 the idea is you query by the id, you get the thing,
01:21 but you can't easily ask it questions like
01:25 what is the average price of the order
01:28 of all the customers stored in your key value store.
01:31 Now, there are ways to add like additional metadata
01:34 that you can stick on to them, so you can sort of fake it a little bit on some of them
01:38 but in general, I can ask for the thing by a key
01:42 and I get a blob that's opaque to the database back.
01:45 Now, these are not great as databases in terms of general purpose databases
01:49 because you can't ask them a wide variety of interesting questions.
01:53 However, they are great in terms of this cluster ability
01:56 of the distributed cash type of thing there is super, super fast,
02:01 because every single query is just finally one item
02:04 by primary key and get it back to me
02:08 so if you horizontally scale that out, you can find
02:10 which key range maps to which server,
02:12 go to that server get it by id— boom, super, super fast.
02:15 So these are nice, they are often used for caches and things like this.
02:19 Next, we have what I think is the real sweet spot for NoSQL databases,
02:25 the ones that potentially could replace
02:27 traditional relational databases in your application,
02:30 that is they are flexible and powerful enough to be general purpose databases
02:35 and that's the document databases.
02:37 So this is MongoDB, CouchDB, OrientDB,
02:40 DocumentDB from Microsoft Azure, things like that,
02:43 so this is really where we going to focus
02:46 almost this entire class, so we'll come back to this.
02:49 We also have a more interesting type of database
02:52 called a columnar database, traditional relational database systems
02:56 like MySQL, Microsoft SQL server etc, store data in rows,
03:01 but a column oriented database is different
03:04 in that it stores data and its tables as columns instead of rows;
03:07 so it's in a lot of ways really similar to relational databases,
03:11 but you'll find that it's easier to kind of associate
03:14 what you might think of is like a pre-joint data,
03:16 maybe some orders, and maybe the orders have order items
03:19 and there's a bunch of those, so you might have one order
03:22 with multiple items, it's easier to group those together in a columnar database.
03:26 But they're kind of more or less like relational databases in a lot of ways.
03:30 So these I believe are the three types of NoSQL databases.
03:32 There's a fourth that often gets grouped here,
03:35 so let's talk about it— graph databases.
03:37 So graph databases let you model relationships
03:40 on many, many small interconnected things
03:44 so think of like social graphs, friends, the pictures,
03:48 the people who have shared that picture, you've liked that picture,
03:52 the friends of your friends who have liked that particular picture
03:55 you can traverse these relationships incredibly easy in graph databases
03:59 because you can actually query directly on the relationships.
04:03 Show all the things related in this way to this item and so on,
04:06 but that does not lead to this cluster friendly sort of thing,
04:09 in fact, this leads to being even more tightly connected
04:12 the less easy to map across multiple
04:15 horizontally scaled servers and things like that.
04:18 So in my mind, the graph databases are super interesting
04:21 but they're not NoSQL they're just not-SQL.
04:25 So that leaves us with three types—
04:27 key value stores, document databases and columnar databases.
04:30 So let's now continue on to talk about document databases.