MySQL復合分區

到底還是開源軟件，MySQL對復合分區的支持遠遠沒有Oracle豐富。

在MySQL 5.6版本中，只支持RANGE和LIST的子分區，且子分區的類型只能為HASH和KEY。

譬如：

CREATE TABLE ts (id INT, purchased DATE)
    PARTITION BY RANGE( YEAR(purchased) )
    SUBPARTITION BY HASH( TO_DAYS(purchased) )
    SUBPARTITIONS 2 (
        PARTITION p0 VALUES LESS THAN (1990),
        PARTITION p1 VALUES LESS THAN (2000),
        PARTITION p2 VALUES LESS THAN MAXVALUE
    );

上述創建語句中，最外層是RANGE分區，分為3個區，里面是HASH子分區，分為2個區，這樣，該表一共分了3*2=6個分區。

當然，也可以用SUBPARTITION語句來顯示定義子分區。

CREATE TABLE ts (id INT, purchased DATE)
    PARTITION BY RANGE( YEAR(purchased) )
    SUBPARTITION BY HASH( TO_DAYS(purchased) ) (
        PARTITION p0 VALUES LESS THAN (1990) (
            SUBPARTITION s0,
            SUBPARTITION s1
        ),
        PARTITION p1 VALUES LESS THAN (2000) (
            SUBPARTITION s2,
            SUBPARTITION s3
        ),
        PARTITION p2 VALUES LESS THAN MAXVALUE (
            SUBPARTITION s4,
            SUBPARTITION s5
        )
    );

注意：

1> 如果你在分區中使用了SUBPARTITION語句，則每個分區中都必須定義，且每個分區中子分區的數量必須保持一致。譬如以下兩種用法就會報錯：

CREATE TABLE ts (id INT, purchased DATE)
    PARTITION BY RANGE( YEAR(purchased) )
    SUBPARTITION BY HASH( TO_DAYS(purchased) ) (
        PARTITION p0 VALUES LESS THAN (1990) (
            SUBPARTITION s0,
            SUBPARTITION s1
        ),
        PARTITION p1 VALUES LESS THAN (2000) (
            SUBPARTITION s2
        ),
        PARTITION p2 VALUES LESS THAN MAXVALUE (
            SUBPARTITION s3,
            SUBPARTITION s4
        )
    );

CREATE TABLE ts (id INT, purchased DATE)
    PARTITION BY RANGE( YEAR(purchased) )
    SUBPARTITION BY HASH( TO_DAYS(purchased) ) (
        PARTITION p0 VALUES LESS THAN (1990) (
            SUBPARTITION s0,
            SUBPARTITION s1
        ),
        PARTITION p1 VALUES LESS THAN (2000),
        PARTITION p2 VALUES LESS THAN MAXVALUE (
            SUBPARTITION s2,
            SUBPARTITION s3
        )
    );

2> 在SUBPARTITION語句中，可指定該分區的物理位置。譬如：

CREATE TABLE ts (id INT, purchased DATE)
    PARTITION BY RANGE(YEAR(purchased))
    SUBPARTITION BY HASH( TO_DAYS(purchased) ) (
        PARTITION p0 VALUES LESS THAN (1990) (
            SUBPARTITION s0a
                DATA DIRECTORY = '/disk0'
                INDEX DIRECTORY = '/disk1',
            SUBPARTITION s0b
                DATA DIRECTORY = '/disk2'
                INDEX DIRECTORY = '/disk3'
        ),
        PARTITION p1 VALUES LESS THAN (2000) (
            SUBPARTITION s1a
                DATA DIRECTORY = '/disk4/data'
                INDEX DIRECTORY = '/disk4/idx',
            SUBPARTITION s1b
                DATA DIRECTORY = '/disk5/data'
                INDEX DIRECTORY = '/disk5/idx'
        ),
        PARTITION p2 VALUES LESS THAN MAXVALUE (
            SUBPARTITION s2a,
            SUBPARTITION s2b
        )
    );

以上這個創建語句，將不同的分區分布到不同的物理路徑下，無疑會極大的分散IO，這一點還是蠻吸引人的。

可惜，在本機測試過程中，報“ERROR 1030 (HY000): Got error -1 from storage engine”錯誤，具體原因還不太清楚，懷疑是MySQL的bug。

參考：

http://dev.mysql.com/doc/refman/5.6/en/partitioning-subpartitions.html

http://dev.mysql.com/doc/refman/5.6/en/tablespace-placing.html