How does subpartitioning actually work and what physical files are created?

Question

I can't understand how the subpartitioning works in mysql.
I am reading the following example:

create table invoices (  
customer_id int not null,    
product_id int not null,    
amount decimal (8,2) not null,    
entry_date date not null default '2006-01-01',   
store_id int not null   
)  
partition by range (year(entry_date))  
subpartition by hash(customer_id)  
subpartitions 4 (  
partition p0 values less than (2008),   
partition p1 values less than (2009),   
partition p2 values less than (2010),  
partition p3 values less than (2011),  
partition plast values less than MAXVALUE  
);  

I can not understand or visualize how this is formed in the HD.
I think that 4 * 5 = 20 physical files are created. Is this correct?
And what data are stored together? Is there a "clustering" of 2008 dates for all customers with the same hash? I am confused on that. Also I am confused how the data are fetched.
Is the customer_id hash used first to determine the range partition or the opposite. What are the exact steps to fetch the data?

UPDATE
Another example. I did the following:

mysql> create table nums_composite (  
    -> id int, happened datetime not null,  
    -> primary key (id, happened)  
    -> ) engine=InnoDB   
    -> partition by range (hour(happened))  
    -> subpartition by hash(id) subpartitions 2  
    -> (  
    -> partition p0 values less than (10),  
    -> partition p1 values less than (20),  
    -> partition p2 values less than MAXVALUE  
    -> );  
Query OK, 0 rows affected (0.28 sec)  


mysql> select partition_name, subpartition_name as sub, partition_method as method,   partition_description ,table_rows from information_schema.partitions where table_name='nums_composite';  
+----------------+-------+--------+-----------------------+------------+  
| partition_name | sub   | method | partition_description | table_rows |  
+----------------+-------+--------+-----------------------+------------+  
| p0             | p0sp0 | RANGE  | 10                    |         17 |  
| p0             | p0sp1 | RANGE  | 10                    |         24 |  
| p1             | p1sp0 | RANGE  | 20                    |         20 |  
| p1             | p1sp1 | RANGE  | 20                    |         17 |  
| p2             | p2sp0 | RANGE  | MAXVALUE              |         13 |  
| p2             | p2sp1 | RANGE  | MAXVALUE              |          9 |  
+----------------+-------+--------+-----------------------+------------+  
6 rows in set (0.00 sec)  

It seems that I am right it creates hash_no* subpartition files but where are they?

root@jim-Linux:/# find . -iname "*_composite*"  
./var/lib/mysql/partioning_chapter_test/nums_composite.frm  
./var/lib/mysql/partioning_chapter_test/nums_composite.par   

Why can't I see the actual files?

Answer 1

Sample in Windows

I ran the following on my Laptop in MySQL 5.6.15

mysql> use test
Database changed
mysql> drop table if exists nums_composite;
Query OK, 0 rows affected (0.70 sec)

mysql> create table nums_composite (
    -> id int, happened datetime not null,
    -> primary key (id, happened)
    -> ) engine=InnoDB
    -> partition by range (hour(happened))
    -> subpartition by hash(id) subpartitions 2
    -> (partition p0 values less than (10),
    -> partition p1 values less than (20),
    -> partition p2 values less than MAXVALUE);
Query OK, 0 rows affected (1.91 sec)

mysql> show create table nums_composite\G
*************************** 1. row ***************************
       Table: nums_composite
Create Table: CREATE TABLE `nums_composite` (
  `id` int(11) NOT NULL DEFAULT '0',
  `happened` datetime NOT NULL,
  PRIMARY KEY (`id`,`happened`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
/*!50100 PARTITION BY RANGE (hour(happened))
SUBPARTITION BY HASH (id)
SUBPARTITIONS 2
(PARTITION p0 VALUES LESS THAN (10) ENGINE = InnoDB,
 PARTITION p1 VALUES LESS THAN (20) ENGINE = InnoDB,
 PARTITION p2 VALUES LESS THAN MAXVALUE ENGINE = InnoDB) */
1 row in set (0.01 sec)

mysql>

I went to the OS and ran the following:

C:\>cd \MySQL_5.6.15\data\test

C:\MySQL_5.6.15\data\test>dir nums_comp*
 Volume in drive C is TI10665200H
 Volume Serial Number is A273-2EFF

 Directory of C:\MySQL_5.6.15\data\test

08/31/2014  04:09 PM            98,304 nums_composite#p#p0#sp#p0sp0.ibd
08/31/2014  04:09 PM            98,304 nums_composite#p#p0#sp#p0sp1.ibd
08/31/2014  04:09 PM            98,304 nums_composite#p#p1#sp#p1sp0.ibd
08/31/2014  04:09 PM            98,304 nums_composite#p#p1#sp#p1sp1.ibd
08/31/2014  04:09 PM            98,304 nums_composite#p#p2#sp#p2sp0.ibd
08/31/2014  04:09 PM            98,304 nums_composite#p#p2#sp#p2sp1.ibd
08/31/2014  04:09 PM             8,594 nums_composite.frm
08/31/2014  04:09 PM                96 nums_composite.par
               8 File(s)        598,514 bytes
               0 Dir(s)  686,691,409,920 bytes free

C:\MySQL_5.6.15\data\test>

Reason you cannot see the files ?

I can see my data files because I have innodb_file_per_table enabled by default in MySQL 5.6.

mysql> show global variables like 'innodb_file_per_table';
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| innodb_file_per_table | ON    |
+-----------------------+-------+
1 row in set (0.00 sec)

mysql>

In your case, you must have innodb_file_per_table disabled. The actual table was inside the system tablespace file ibdata1 (usually located in /var/lib/mysql)

My Guess

• You are using a version before MySQL 5.6
• innodb_file_per_table is set to 0 because of one of the following:
  • You are running on defaults (no my.cnf)
  • You have my.cnf with innodb_file_per_table=0

How to fix this:

STEP #1 : Enable innodb_file_per_table

Add this to the my.cnf

innodb_file_per_table=1

STEP 2 : Restart mysql

service mysql restart

STEP 3 : Regenerate the table

CREATE TABLE nums_composite_new LIKE nums_composite;
INSERT INTO nums_composite_new SELECT * FROM  nums_composite;
ALTER TABLE nums_composite RENAME nums_composite_old;
ALTER TABLE nums_composite_new RENAME nums_composite;
DROP TABLE nums_composite_old;

The .ibd files should now be visible

GIVE IT A TRY !!!

UPDATE 2014-08-31 16:37 EDT

You asked me

I am in ubuntu.Does it change anything?

The only thing that changes is where my.cnf should be. Run this

ls -l /etc/mysql/my.cnf

If the file exists, open it in an editor and add innodb_file_per_table=1 under the [mysql] header

If the file does not exist, run this

echo "[mysqld]" > /etc/mysql/my.cnf
echo "innodb_file_per_table=1" >> /etc/mysql/my.cnf

Then, you can do STEP 2 and STEP 3