How to decide varchar partition RANGE in MySQL 5.5? - mysql

Question

Backgroud
I have a very big table, the table is just like this
CREATE TABLE tb_doc (
did mediumint(8) unsigned NOT NULL auto_increment,
title varchar(80) NOT NULL default '',
...,
PRIMARY KEY (did),
KEY title (title)
)
TYPE=MyISAM;
The type of title is varchar(80), most of the time title will be pure number strings like '111111','2222222','44444444', some times it will be utf-8 strings, like '3a','a4' or "中国" (Chinese characters).
I've already used HASH (did) to do partition, but my SELECT statements are alway like
SELECT did, title,... FROM tb_doc WHERE title= '1111111';
SELECT did, title,... FROM tb_doc WHERE title= '2222222';
So I want to use title to do partition, hope this would be faster. Now it comes the question.
Experiment
I used the following statement:
PARTITION BY RANGE COLUMNS (title)(
PARTITION p00 VALUES LESS THAN (1), # not pure number strings
PARTITION p01 VALUES LESS THAN (500000), # pure number strings from 1 to 500k
PARTITION p02 VALUES LESS THAN (1000000), # pure number strings from 500k to 1000k
PARTITION p03 VALUES LESS THAN (1500000), # pure number strings from 1000k to 1500k
.......... # ......
PARTITION pn VALUES LESS THAN (25000000), # the biggest number now
)
;
Similar Questions
I read the following two Q&As:
Partitioning a database table in MySQL
How to Partitioning a table using a LIKE criteria in Mysql
but they are for English world, not work in my situation.
Questions
Use title to do partition is better, right?
Can you give me a "utf-8" RANGE example?
I tryied '500000','1000000',...,but they do not work.
If I use SELECT xxx from tb_doc WHERE title='12345', dose MySQL fetch data from partation 1 only?
This table is ~50GB, how many partitions are optimum?
Thank you in advance.

Answer 1

May I note that VARCHAR will have problems with storing characters from multiple languages properly, better use NVARCHAR.
HASH partitioning is used to distribute load over partitions evenly. I would say, that first you should partition by something meaningful to a human (columns appearing in Where clause often) and then do HASH sub-partitioning to utilise as many cores as possible at the same time. So number of HASH sub-partitiong in this case will <= No cores.
I would suggest you creating a clustered index on title column. This will speed up your queries.
And in relation to your questions:
Not neceserally. It will speed up queries, because of clustered index, not partitioning.
Use partitioning to manage the table: eg. delete many rows quickly.
If a good proportion of your queries looks for many rows (not just 1) or title is not a UNIQUE column, then you may consider Partition
As an example of UTF-8 partition boundary I would say: less then ('c')
Depending on how you define partitioning it may hit 1, several or all partitions.
There is no penalty for having many partitions, but a table in MySQL 5.5+ can have upto 1024 partitions and sub-partitions.
When you whan to do partitioning by string value, use KEY PARTITIONING as described here: 18.2.5. KEY Partitioning.
Example:
CREATE TABLE tm1 (
s1 CHAR(32) PRIMARY KEY
)
PARTITION BY KEY(s1)
PARTITIONS 10;
Set number of partitions same as there are letters in your alphabet (or all alphabets you anticipate to see in the table) to begin with.

Answer 2

Partitioning by title, even if you could do it, will not speed up
SELECT did, title,... FROM tb_doc WHERE title= '1111111';
For a further discussion of the limitations of PARTITIONing, plus what few use cases it will help, see my blog;