Efficient way to DELETE whole partition's data in table partitioned by HASH(DAY(datetime))?

Question

I have a MySQL InnoDB table PARTITIONed by HASH(DAY(dateTime)). I'd like to remove partitions holding data older than 10 days.

CREATE TABLE `partitioned` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `dateTime` datetime NOT NULL,
  `sourceId` int(10) unsigned NOT NULL,
  `destinationId` int(10) unsigned NOT NULL,
  `times` int(10) unsigned NOT NULL,
  PRIMARY KEY (`id`,`dateTime`),
  UNIQUE KEY `key` (`dateTime`,`sourceId`,`destinationId`) USING BTREE,  
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8
PARTITION BY HASH(DAY(`dateTime`)) PARTITIONS 31

I've tried some queries:

EXPLAIN PARTITIONS SELECT * FROM `partitioned` WHERE DAY(`dateTime`) IN (1,2,3,4);
EXPLAIN PARTITIONS SELECT * FROM `partitioned` WHERE `dateTime` < '2015-01-01';

EXPLAIN for those two is showing that all partitions will be inspected. Not good!

EXPLAIN PARTITIONS SELECT * FROM `partitioned` WHERE `dateTime` IN ('2015-01-01','2015-01-02','2015-01-03','2015-01-04');

EXPLAIN for this one is showing that only required partitions will be inspected. I suppose that DELETE will also touch only required partitions, right?

Questions are:

• So, what is the fastest available way to DELETE from table partitioned by HASH?
• Is it possible to get name of partition holding DAY? Which function is MYSQL using for partitioning using HASH(DAY())?

Or it is a bad idea and I should move to RANGE partitioning with DROPing and CREATing partitions on daily basis?

UPD: I see http://dev.mysql.com/doc/refman/5.5/en/alter-table-partition-operations.html that for MySQL >= 5.5.0 it is possible to TRUNCATE PARTITION, but what if I have AUTO_INCREMENT field in partitioned table? Is TRUNCATE PARTITION reseting auto_increment field or what?

UPD2: I'll try to answer my question. Ok, we can get name of partition by EXPLAIN PARTITIONS SELECT * FROM partitioned WHERE dateTime IN ("2011-01-01"). As soon as we know name of partition, we can do ALTER TABLE partitioned TRUNCATE PARTITION {partitionName}, right? Is it a good way, what do you think?

Answer 1

To answer the update, the TRUNCATE PARTITION will not reset the auto_increment field. This makes sense since it would be sticky to handle in relation to the other partitions in the auto increment scenario.

However, a table truncate will reset the auto increment key.