Additional sql optimization for drupal

[jeff1evesque]

After #464, we will optimize our database implementation, by creating puppet equivalent logic:

• change the overall transaction isolation (i.e. tx_isolation) on the sql database from REPEATABLE-READ to READ-COMMITTED:

SET tx_isolation = 'READ-COMMITTED';

• Move semaphore sql table implementation from innodb to memory:

MariaDB [db_drupal]> ALTER TABLE semaphore ENGINE = MEMORY;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [db_drupal]> ALTER TABLE semaphore DROP PRIMARY KEY;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [db_drupal]> ALTER TABLE semaphore ADD PRIMARY KEY (name, value) USING BTREE;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [db_drupal]> ALTER TABLE semaphore ADD UNIQUE name (name) USING BTREE;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [db_drupal]> ALTER TABLE semaphore DROP INDEX value;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [db_drupal]> ALTER TABLE semaphore ADD INDEX value (value) USING BTREE;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [db_drupal]> ALTER TABLE semaphore DROP INDEX expire;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [db_drupal]> ALTER TABLE semaphore ADD INDEX expire (expire) USING BTREE;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [db_drupal]> show table status where Name = 'semaphore';
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

Note: the following indicates the motivation for implementing the memory engine, instead of innodb, for the drupal semaphore table:

Drupal supports multiple database backends, but both MEMORY and the concept of storage engines as a whole is MySQL specific. Therefore, the Schema API has no support for specifying the storage engine.