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テーブルを一時的にロックして、他の同時プロセスが変更を加えないようにしたいと考えています。これは、このテーブルが一時テーブルにコピーされ、変更されてからコピーされるためです (元のテーブルは実際には削除され、新しいテーブルの名前が変更されます)。次に、これがすべて完了したら、テーブルのロックを解除し、ロック中に試行されたものを再開したいと考えています。

また、新しいテーブルを構築するためにロックされたテーブルから読み取ることができる必要があります。

これが私が試したものですが、うまくいかないようです。

$mysqli = new mysqli(DB_HOST, DB_USER, DB_PASSWORD, DB_NAME, DB_PORT);

$mysqli->autocommit(false)

// create a table to hold parts to keep
$q1 = "CREATE TABLE new_table LIKE my_table;";
$res1 = $mysqli ->query($q1);       

// Lock table to avoid concurrent update issues
$q2 = "LOCK TABLE my_table WRITE;";
$res2 = $mysqli ->query($q2);           

// Insert data to keep into new table   
$q3 = "INSERT INTO new_table SELECT * FROM my_table WHERE some_id IN (SELECT ID FROM table2)";
$res3 = $mysqli ->query($q3);

// drop original table
$q4 = "DROP TABLE my_table;";
$res4 = $mysqli ->query($q4);

// rename new table
$q5 = "RENAME TABLE new_table TO my_table;";
$res5 = $mysqli ->query($q5);

$mysqli ->commit(); // commit changes and re-enable autocommit

$q = "UNLOCK TABLES;";
$res = $mysqli ->query($q);

PHPmyadmin を使用してテストするために、「SET AUTOCOMMIT=0; LOCK TABLE my_table WRITE;」を発行しました。クエリを実行してから、my_table から何かを削除しようとしたところ、削除できました。これをブロックしたい。また、lock ステートメントを発行した後、残りの手順は失敗し、何も変更されません。

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Sorry for the long answer, but this will need to be answered in multiple parts.

1. On locking InnoDB tables with LOCK TABLES in general

Using LOCK TABLES with InnoDB does in fact work, and can be demonstrated with two instances of the MySQL CLI connected to the same server (denoted by mysql-1 and mysql-2) in the below example. It should generally be avoided in any sort of production context because of the impact to clients, but sometimes it can be the only option.

Create a table and populate it with some data:

mysql-1> create table a (id int not null primary key) engine=innodb;
Query OK, 0 rows affected (0.02 sec)

mysql-1> insert into a (id) values (1), (2), (3);
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

Lock the table:

mysql-1> lock tables a write;
Query OK, 0 rows affected (0.00 sec)

Try to insert from mysql-2, which will hang waiting on the lock:

mysql-2> insert into a (id) values (4);

Now unlock the table from mysql-1:

mysql-1> unlock tables;
Query OK, 0 rows affected (0.00 sec)

And finally mysql-2 unblocks and returns:

Query OK, 1 row affected (6.30 sec)

2. Using phpMyAdmin for testing

Your testing method using phpMyAdmin is invalid because phpMyAdmin does not maintain a persistent connection to the server between queries from its web interface. In order to use any sort of locking LOCK TABLES, START TRANSACTION, etc., you need to maintain a connection while the locks are held.

3. Locking all tables needed during work

The way that MySQL locks tables, once you have used LOCK TABLES to explicitly lock anything, you will not be able to access any other tables that were not locked explicitly during the LOCK ... UNLOCK session. In your above example, you need to use:

LOCK TABLES my_table WRITE, new_table WRITE, table2 READ;

(I am assuming table2 used in the subselect was not a typo.)

4. Atomic table swap using RENAME TABLE

Additionally, I should note that replacing the existing table using DROP TABLE followed by RENAME TABLE will cause a brief moment where the table does not exist, and this may confuse clients that expect it to exist. It is generally much better to do:

CREATE TABLE t_new (...);
<Populate t_new using some method>
RENAME TABLE t TO t_old, t_new TO t;
DROP TABLE t_old;

This will perform an atomic swap of the two tables.

于 2013-01-12T22:50:40.440 に答える