partitioning by data mysql - mysql

Question

I have table 'items'. 18 mln records:
CREATE TABLE IF NOT EXISTS `items` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`log_id` int(11) NOT NULL,
`res_id` int(11) NOT NULL,
`link` varchar(255) NOT NULL,
`title` text NOT NULL,
`content` text NOT NULL,
`n_date` varchar(255) NOT NULL,
`nd_date` int(11) NOT NULL,
`s_date` int(11) NOT NULL,
`not_date` date NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `link_2` (`link`),
KEY `log_id` (`log_id`),
KEY `res_id` (`res_id`),
KEY `now_date` (`not_date`),
KEY `sql_index` (`res_id`,`id`,`not_date`)
) ENGINE=Aria DEFAULT CHARSET=utf8 PAGE_CHECKSUM=0 AUTO_INCREMENT=18382133 ;
Trying to partition this table I created a mini copy of it and include column 'not_date' in primary and uniq keys:
CREATE TABLE IF NOT EXISTS `part_items` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`log_id` int(11) NOT NULL,
`res_id` int(11) NOT NULL,
`link` varchar(255) NOT NULL,
`title` text NOT NULL,
`content` text NOT NULL,
`n_date` varchar(255) NOT NULL,
`nd_date` int(11) NOT NULL,
`s_date` int(11) NOT NULL,
`not_date` date NOT NULL,
PRIMARY KEY (`not_date`,`id`),
UNIQUE KEY `link_2` (`not_date`,`link`),
KEY `log_id` (`log_id`),
KEY `res_id` (`res_id`),
KEY `now_date` (`not_date`),
KEY `sql_index` (`res_id`,`id`,`not_date`)
) ENGINE=Aria DEFAULT CHARSET=utf8 PAGE_CHECKSUM=0
/*!50100 PARTITION BY RANGE ( TO_DAYS(not_date))
(PARTITION p_1 VALUES LESS THAN (735963) ENGINE = Aria,
PARTITION p_2 VALUES LESS THAN (736694) ENGINE = Aria) */ AUTO_INCREMENT=18414661 ;
Then I run sql_query:
alter table `part_items` PARTITION BY RANGE( TO_DAYS(not_date) ) (
PARTITION p_1 VALUES LESS THAN( TO_DAYS('2014-12-31') ),
PARTITION p_2 VALUES LESS THAN( TO_DAYS('2016-12-31') )
);
Then I trying to select records that must de in p_1 and explain partitions show me that searching was only in p_1. But when I select records that must be in p_2 explain partitions show full-scan(p_1,p_2).
What wrong in my code?
Queries:
explain partitions SELECT * FROM `part_items` where content like '%k%' and not_date < '2014-05-12'
explain partitions SELECT * FROM `part_items` where content like '%k%' and not_date > '2015-01-01'
And one more question: Is it possible to partitioning views?

Answer 1

When PARTITIONing by some date function, there is a chance of an invalid date being provided. That would lead to NULL; such values are stored in the first partition.
This is an issue that has tripped up many a developer. The typical 'workaround' is to have the first partition empty so that the effort of looking in it is (usually) minimal. In your case:
PARTITION p_0 VALUES LESS THAN(0)
Partitioning on less than about 6 partitions is usually not worth the effort; will you be adding more partitions?
(Caveat: My advice comes from years of MyISAM/InnoDB partitioning; I don't know of Aria works differently. I suspect that partitioning is mostly handled at then Engine-independent layer.)