How does subpartitioning actually work and what physical files are created?
-
21-10-2020 - |
سؤال
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?
المحلول
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
withinnodb_file_per_table=0
- You are running on defaults (no
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