Questions about FriendFeed's MySql SchemaLess Design - mysql

Question

Bret Taylor discussed the SchemaLess Design in this blog post: http://bret.appspot.com/entry/how-friendfeed-uses-mysql
It looks like they stored different class's Objects into only one table.Then build more index tables.
my question is that how to build index on one class.
for example, a user's blog is {id,userid,title,body}. A user's tweet is {id,userid,tweet}.
If I want to build an index for users' blogs how can I do?

Answer 1

It's very simple -- perhaps simpler than you expect.
When you store a blog entity, you're going to insert to the main entities table of course. A blog goes like this:
CREATE TABLE entities (
id INT AUTO_INCREMENT PRIMARY KEY,
entity_json TEXT NOT NULL
);
INSERT INTO entities (id, entity_json) VALUES (DEFAULT,
'{userid: 8675309,
post_date: "2010-07-27",
title: "MySQL is NoSQL",
body: ... }'
);
You also insert into a separate index table for each logical type of attribute. Using your example, the userid for a blog is not the same as a userid for a tweet. Since you just inserted a blog, you then insert into index table(s) for blog attribute(s):
CREATE TABLE blog_userid (
id INT NOT NULL PRIMARY KEY,
userid BIGINT UNSIGNED,
KEY (userid, id)
);
INSERT INTO blog_userid (id, userid) VALUES (LAST_INSERT_ID(), 8675309);
CREATE TABLE blog_date (
id INT NOT NULL PRIMARY KEY,
post_date DATETIME UNSIGNED,
KEY (post_date, id)
);
INSERT INTO blog_date (id, post_date) VALUES (LAST_INSERT_ID(), '2010-07-27');
Don't insert into any tweet index tables, because you just created a blog, not a tweet.
You know all rows in blog_userid reference blogs, because that's how you inserted them. So you can search for blogs of a given user:
SELECT e.*
FROM blog_userid u JOIN entities e ON u.id = e.id
WHERE u.userid = 86765309;
Re your comment:
Yes, you could add real columns to the entities table for any attributes that you know apply to all content types. For example:
CREATE TABLE entities (
id INT AUTO_INCREMENT PRIMARY KEY,
entity_type INT NOT NULL,
creation_date TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
entity_json TEXT NOT NULL
);
The columns for entity_type and creation_date would allow you to crawl the entities in chronological order (or reverse chronological order) and know which set of index tables matches the entity type of a given row.

Answer 2

They do not store objects of different classes in the same table. The 'entities' table they are referring to is used to store only one kind of entities.
For example, a typical entity in FriendFeed might look like this:
"id": "71f0c4d2291844cca2df6f486e96e37c",
"user_id": "f48b0440ca0c4f66991c4d5f6a078eaf",
"feed_id": "f48b0440ca0c4f66991c4d5f6a078eaf",
"title": "We just launched a new backend system for FriendFeed!",
"link": "http://friendfeed.com/e/71f0c4d2-2918-44cc-a2df-6f486e96e37c",
"published": 1235697046,
"updated": 1235697046,
To understand the implementation better, have a look at the example given here: https://github.com/jamesgolick/friendly#readme