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Problem: I have two fairly large tables. A 'wall' table for messages between users with 9 million rows at 2 GB and a 'chapter' table at 2 million rows and 18 GB. I want to keep the number of active rows for the 'wall' table small while I want to diminish the size of the chapter table. I made the mistake of not compressing text data to begin with and I'd like to start compressing data in the archives.

For the 'wall' table, I'm thinking that everything older than a certain wall id will be transferred and compressed to a 'wall_archive'. Anyone wanting to view older posts will just be given a "view archive" link where older post queries use the archive table. Then I run a cron job to do this every now and then and the last wall id archived will be stored somewhere for reference. Am I going the right direction here?

I'm not so sure how to keep the 'chapter' table manageable. Perhaps it's less archiving and more needing to partition the table (or both). But what's the best way to do this? I was thinking of splitting 'story' IDs into odds and evens and dividing the chapter into two tables but I'll run into the same problem again down the road. Or I can archive stories modified before a certain date. Or before a certain story ID. Any suggestions for a scalable solution?

Lastly, how should I go about compressing text data? Should I use PHP's gzcompress function at level 9 to store text data into a BLOB column then gzuncompress the data on retrieval? Or should I use MySql's COMPRESS/UNCOMPRESS functions? I'm leaning towards using PHP in case I separate the web server(s) from the DB server where I can have PHP do the compression processes instead of the more valuable DB server but I'd like to know what best practices are.

Considerations: I'll still need to be able to access old 'chapter' data easily. 'wall' data can be put into slower storage if needed but it isn't necessary at the moment.

Environment: 6 Core AMD Opteron, 16 GB RAM, 256 GB SSD for MySql, Percona Server 5.5, Apache, CentOS 6, PHP 5.3, innodb_file_per_table is enabled, database and webserver is running on same machine, total database size is 30 GB, all tables are InnoDB

Schemas:

CREATE TABLE `wall` (
  `id_wall` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `id_author` int(10) unsigned NOT NULL 
     COMMENT 'wall''s owner',
  `id_user` int(10) unsigned NOT NULL DEFAULT '0'
     COMMENT 'user that wrote the comment',
  `comment` text NOT NULL,
  `created` datetime NOT NULL,
  PRIMARY KEY (`id_wall`),
  KEY `id_user` (`id_user`),
  KEY `id_author` (`id_author`)
) ENGINE=InnoDB
  DEFAULT CHARSET=utf8
  COMMENT='User profile wall'
  AUTO_INCREMENT=9710655 ;

CREATE TABLE IF NOT EXISTS `chapter` (
  `id_story` int(11) unsigned NOT NULL,
  `id_chapter` int(11) unsigned NOT NULL DEFAULT '0',
  `title` varchar(255) NOT NULL,
  `main_image` varchar(2047) DEFAULT NULL,
  `body` mediumtext,
  `created` datetime NOT NULL,
  `modified` datetime NOT NULL,
  `is_not_shown` tinyint(1) NOT NULL DEFAULT '0',
  PRIMARY KEY (`id_story`,`id_chapter`)
) ENGINE=InnoDB
  DEFAULT CHARSET=utf8
  ROW_FORMAT=DYNAMIC
  COMMENT='Story content by chapter';

ALTER TABLE `chapter`
  ADD CONSTRAINT `chapter_ibfk_1` 
    FOREIGN KEY (`id_story`) 
    REFERENCES `story` (`id_story`) 
    ON DELETE CASCADE 
    ON UPDATE CASCADE;
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Do you expect your data to grow fast? A couple of GB is not that much nowadays. If the size is no real problem simply do not compress at all. –  mdo Jul 22 '12 at 11:58
    
It's actually the 'chapter' table size that I'd like to reduce since it's getting harder to make schema changes. I'm also making a move to Intel 710 SSDs which my host only has in a 100 GB option so it's also a space consideration. –  Jason Ado Jul 22 '12 at 13:02
    
Seems like you would be through making schema changes by now. Consider making parallel tables if you must add columns. –  Rick James Jul 24 '12 at 0:05

2 Answers 2

Performance

I would develop analytics that tell me how frequently older data is accessed and by what date intervals. If very few people look at anything older than 1 month, your options are numerous. If it's all over the board, that will be a different strategy.

Let's pretend that content older than 1 month is only accessed occasionally, say < 2% of the requests. Two options available to you include: partitioning and horizontal sharding, both by date. With partitioning, you simply partition by RANGE using the 'created' field in your table. With horizontal sharding you do the same thing, except using a cron job or event to create a new periodic version of your table, then migrate rows to the periodic table. With horizontal sharding, you could use UNION statements to span multiple tables.

Partitioning will have little or no effect on your data model. Sharding will require data model intelligence.

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For compressing...

Do it in the client; that will lead to less traffic between client and server. (OK, they are on the same machine, so this is not much of an issue.)

Use PHP's gzcompress, gzuncomress; don't worry about compression level. Expect about 3:1 compression for regular text.

Yes, the MEDIUMTEXT would need to be MEDIUMBLOB.

Don't "archive" old data; you have not justified the need for it (yet). Caching will generally take care of making 'recent' chapters faster.

Check out Facebook and Percona for "online alters".

innodb_buffer_pool_size should be about 70% of available ram.

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