MySQL using partitioning and keeping primary keys unchanged - mysql

Question

I'm using MySQL 5.5, and I have an existing table in production that stores customer transactions. A simplified version of the table is:
CREATE TABLE transactions (
id INT NOT NULL AUTO_INCREMENT,
description CHAR(100),
posted DATE,
PRIMARY KEY (id)
) ENGINE=MyISAM
We are exploring the idea of using partitioning on the transaction date to make reports that use date filtering execute faster. The following attempt fails because of restrictions on primary keys and partitions explained in MySQL Partitioning Keys documentation.
mysql> CREATE TABLE transactions (
-> id INT NOT NULL AUTO_INCREMENT,
-> description CHAR(100),
-> posted DATE,
-> PRIMARY KEY (id)
-> ) ENGINE=MyISAM
-> PARTITION BY HASH(MONTH(posted)) PARTITIONS 12;
ERROR 1503 (HY000): A PRIMARY KEY must include all columns in the table's partitioning function
A possible workaround is as follows:
CREATE TABLE transactions (
id INT NOT NULL AUTO_INCREMENT,
description CHAR(100),
posted DATE,
PRIMARY KEY (id, posted)
) ENGINE=MyISAM
PARTITION BY HASH(MONTH(posted)) PARTITIONS 12;
Another workaround would be:
CREATE TABLE transactions (
id INT NOT NULL AUTO_INCREMENT,
description CHAR(100),
posted DATE,
KEY (id)
) ENGINE=MyISAM
PARTITION BY HASH(MONTH(posted)) PARTITIONS 12;
In both workarounds the database would not stop the situation of multiple records with the same id, but different posted dates. Is there any way to use partitioning on the posted field and maintain the original unique constraints?

Answer 1

I've been facing this same "problem", and one workaround that I found for that was splitting my table in two, resulting in something like this in your case:
CREATE TABLE transactions (
id INT NOT NULL AUTO_INCREMENT,
description CHAR(100),
PRIMARY KEY (id)
) ENGINE=MyISAM;
And the other:
CREATE TABLE transactions_date (
id INT NOT NULL,
posted DATE
) ENGINE=MyISAM
PARTITION BY HASH(MONTH(posted)) PARTITIONS 12;
The obvious problem is that you have to add some extra logic to the application, like the need to fetch both tables to retrieve all the data when using SELECT statements. You could probably use triggers to help you with the tasks related to INSERT, UPDATE and DELETE.
Just a note: the only functions that can benefit from the use of partition pruning in DATE or DATETIME columns are: YEAR(), TO_DAYS() and TO_SECONDS() (this last one is only available since MySQL 5.5).