Recently we ran into a wall in one of my customers’ sites. They built an application that processed EDI documents. Each document, contained a list of transactions. Their application would launch a thread for each transaction in the document. On the surface this sounds good and the multi-threaded approach would speed up processing of a document.

InnoDB is the only built-in transactional storage engine and unfortunately has some limitations.

TX1 SET TRANSACTION ISOLATION LEVEL READ COMMITTED
TX2 SET TRANSACTION ISOLATION LEVEL READ COMMITTED
TX1 START TRANSACTION
TX2 START TRANSACTION
TX1 INSERT INTO child
TX2 INSERT INTO child (with same parent)
TX1 UPDATE parent
TX2 UPDATE parent (same parent row)

ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction

We solved this issue using a third party storage engine; solidDB.

Other storage engines available with MySQL

Federated Storage Engine (FSE) allows you to connect to a remote server and “mount” a table on your local server, which links to the data on the remote server, for read-only access.

$ mysql -u root -ppassword -h remote

mysql> CREATE DATABASE test;

mysql> use test;

mysql> CREATE TABLE drivers (id INT,name VARCHAR(100));

mysql> INSERT INTO drivers (id, name) VALUES (1, ‘Chris’);

mysql> INSERT INTO drivers (id, name) VALUES (2, ‘Sheeri’);

mysql> INSERT INTO drivers (id, name) VALUES (3, ‘Elie’);

mysql> select * from drivers;

+------+--------+
| id   | name   |
+------+--------+
|    1 | Chris  |
|    2 | Sheeri |
|    3 | Elie   |
+------+--------+
3 rows in set (0.08 sec)

mysql> exit;

$ mysql -u root -ppassword -h local

mysql> CREATE DATABASE test;

mysql> use test;

mysql> CREATE TABLE drivers (id INT,name VARCHAR(100)) ENGINE=FEDERATED
CONNECTION=’mysql://root:password@remote:3306/test/drivers’;

mysql> select * from drivers;

+------+--------+
| id   | name   |
+------+--------+
|    1 | Chris  |
|    2 | Sheeri |
|    3 | Elie   |
+------+--------+
3 rows in set (0.14 sec)

mysql> exit;

Enjoy FSE tables!

Bye! Thanks for all the fish!

christos@themysqlguy.com

One of the best features of MySQL is the fact that you can

have a log of all queries that take longer than n seconds.

Activating the Log

To activate this log start MySQL with the –log-slow-queries[=file_name] option, or add the previous option to your my.cnf or my.ini and restart the server:

[mysqld]

…

log-slow-queries[=file_name]

You can specify a file name for the slow-query-log or it will be called host_name-slow.log. By default the log is in the data directory, unless you specify an absolute path with the file name.

By default a slow query is one that takes 10 seconds. You can change that by specifying long_query_time in either during startup or in the my.cnf or my.ini file.

[mysqld]

…

log-slow-queries

long_query_time=8

Viewing the Log

The log is in text format and can easily be viewed by any text editor and looks like this:

# Time: 070116  5:16:35

# User@Host: nvusr[nvusr] @ app01 [10.30.5.226]

# Query_time: 21  Lock_time: 0  Rows_sent: 20  Rows_examined: 4078677

SELECT ectransactions.*, interchanges.interchange_datetime as transaction_datetime, interchanges.partner_name, interchanges.direction, functional_groups.functional_group_control_numb, fo_name, functional_organization_qualid, partner_name, partner_qualid, interchanges.interchange_control_number, operators.name as operator_name, trading_participants.name as client_name FROM ectransactions  left join functional_groups ON ectransactions.functional_group_id=functional_groups.id left join interchanges ON ectransactions.interchange_id=interchanges.id left join trading_participants ON ectransactions.trading_participant_id=trading_participants.id left join operators ON ectransactions.operator_id=operators.id  ORDER BY client_name asc, transaction_datetime desc  LIMIT 0, 20;

However, its a lot more readable with the mysqldumpslow command, whose output looks like this:

Count: 1  Time=24.00s (24s)  Lock=0.00s (0s)  Rows=20.0 (20), nvusr[nvusr]@tqapp02

  SELECT ectransactions.*, interchanges.interchange_datetime as transaction_datetime, interchanges.partner_name, interchanges.direction, functional_groups.functional_group_control_numb, fo_name, functional_organization_qualid, partner_name, partner_qualid, interchanges.interchange_control_number, operators.name as operator_name, trading_participants.name as client_name FROM ectransactions  left join functional_groups ON ectransactions.functional_group_id=functional_groups.id left join interchanges ON ectransactions.interchange_id=interchanges.id left join trading_participants ON ectransactions.trading_participant_id=trading_participants.id left join operators ON ectransactions.operator_id=operators.id  ORDER BY transaction_datetime asc, description desc  LIMIT N, N

Count: 2  Time=22.00s (44s)  Lock=0.00s (0s)  Rows=20.0 (40), nvusr[nvusr]@2hosts

  SELECT ectransactions.*, interchanges.interchange_datetime as transaction_datetime, interchanges.partner_name, interchanges.direction, functional_groups.functional_group_control_numb, fo_name, functional_organization_qualid, partner_name, partner_qualid, interchanges.interchange_control_number, operators.name as operator_name, trading_participants.name as client_name FROM ectransactions  left join functional_groups ON ectransactions.functional_group_id=functional_groups.id left join interchanges ON ectransactions.interchange_id=interchanges.id left join trading_participants ON ectransactions.trading_participant_id=trading_participants.id left join operators ON ectransactions.operator_id=operators.id  ORDER BY client_name asc, transaction_datetime desc  LIMIT N, N

I Want More!

You can also have MySQL add all queries that don’t use indexes into the slow-query-log. Add –log-queries-not-using-indexes during startup or in the my.cnf or my.ini file.

Bye! Thanks for all the fish!

christos@themysqlguy.com

Starting out

Once MySQL is installed you should assign a root password to the server, drop the guest account and remove certain built-in databases you don’t need.

$ mysql -u root

mysql> DELETE FROM mysql.user WHERE User = ”;

mysql> UPDATE mysql.user SET Password = PASSWORD(’some_pass’) WHERE User = ‘root’;

mysql> DELETE FROM mysql.user WHERE Host <> ‘localhost’;

mysql> UPDATE mysql.user SET Host = ‘%’;

mysql> create database modes;

mysql> drop database test;

mysql> FLUSH PRIVILEGES;

mysql> quit;

$ mysql -u root -psome_pass

mysql>

$ mysql -u root -p

Enter password:

mysql>

SQL Mode

The SQL Mode you chose is very important because it affects how your MySQL server will behave in certain situations.

By Default it runs in “no mode”. Which is kind of a free-for-all mode. This mode is very forgiving…maybe too forgiving for some “Enterprise” applications.

$ mysql -u root -psome_pass 

mysql> use modes; 

mysql> CREATE TABLE drivers (id TINYINT UNSIGNED, name CHAR(5));

Query OK, 0 rows affected (0.03 sec)

mysql> INSERT INTO drivers (id, name) VALUES (255,’Doug’);

Query OK, 1 row affected (0.02 sec) 

mysql> select * from drivers;

+——+——+

| id   | name |

+——+——+

|  255 | Doug |

+——+——+

1 row in set (0.00 sec) 

mysql> INSERT INTO drivers (id, name) VALUES (259,’Christos’);

Query OK, 1 row affected, 2 warnings (0.00 sec) 

mysql> select * from drivers;

+——+——-+

| id   | name  |

+——+——-+

|  255 | Doug  |

|  255 | Chris |

+——+——-+

2 rows in set (0.00 sec) 

mysql> DROP TABLE drivers;

Query OK, 0 rows affected (0.07 sec) 

mysql> quit; 

To avoid the above scenario, you must assign an SQL Mode to your MySQL server. I like the traditional mode. It would raise an error if you tried to run the above commands.

Add sql_mode=traditional in your my.cnf/my.ini file, restart the server and that will solve the issue. It would give the following results:

$ mysql -u root -psome_pass

mysql> use modes;

mysql> CREATE TABLE drivers (id TINYINT UNSIGNED, name CHAR(5));

Query OK, 0 rows affected (0.03 sec)

mysql> INSERT INTO drivers (id, name) VALUES (255,’Doug’);

Query OK, 1 row affected (0.02 sec)

mysql> select * from drivers;

+——+——+

| id   | name |

+——+——+

|  255 | Doug |

+——+——+

1 row in set (0.00 sec)

mysql> INSERT INTO drivers (id, name) VALUES (259,’Christos’);

ERROR 1264 (22003): Out of range value adjusted for column ‘id’ at row 1

mysql> DROP TABLE drivers;

Query OK, 0 rows affected (0.07 sec)

mysql> quit; 

There are more SQL Modes to choose from. Click here to get a complete list of modes and a more in-depth explanation of each one.

Bye! Thanks for all the fish!