Database-level locking mechanisms are a way to control concurrent access to the database by multiple transactions.

 Are you facing deadlock?

SQLSTATE[HY000]: General error: 1205 Lock wait timeout exceeded; try restarting transaction

To prevent this issue, you can implement locking mechanisms in your application code or database schema to ensure that only one transaction at a time can access the affected resources. For example, you could use row-level locking or table-level locking to prevent concurrent writes to the same table. You could also use optimistic locking, which involves adding a version number or timestamp to each row in the table, to ensure that multiple transactions do not inadvertently overwrite each other's changes.

In addition to locking, you can also consider optimizing your database schema and queries to reduce the duration of transactions and minimize the number of locks being held. This can include techniques such as normalizing your database schema, adding appropriate indexes to your tables, and avoiding long-running queries or transactions.

1. Application level 

Using flock please check example php code below:

$lockFile = '/path/to/lock/file.lock'; $fp = fopen($lockFile, 'w'); if (flock($fp, LOCK_EX)) { // acquire exclusive lock // execute critical section of code // ... flock($fp, LOCK_UN); // release lock } else { // lock could not be acquired } fclose($fp);

2. database-level locking mechanisms

Database-level locking mechanisms are a way to control concurrent access to the database by multiple transactions. These mechanisms help to prevent inconsistencies in the database and ensure data integrity.

Here are several types of database-level locking mechanisms available, including:

 - Row-level locking: This type of locking allows multiple transactions to access different rows in a table simultaneously, but only one transaction can update a particular row at a time.

 - Table-level locking: This type of locking prevents multiple transactions from accessing the same table simultaneously. Only one transaction can access the table at any given time.

 - Database-level locking: This type of locking allows only one transaction to access the entire database at any given time.

 - Pessimistic locking: This type of locking is used when a transaction needs to lock a row or table for a longer period of time. It is typically used when there is a high risk of concurrent access to the same data.

 - Optimistic locking: This type of locking is used when a transaction needs to lock a row or table for a shorter period of time. It is typically used when there is a lower risk of concurrent access to the same data.

Below is MySQL :

1. Row-level locking using SELECT ... FOR UPDATE:

You can use SELECT ... FOR UPDATE to lock specific rows in a table. The following example shows how to lock the row with the id=1 in the 'users' table:

BEGIN; SELECT * FROM users WHERE id = 1 FOR UPDATE; -- perform some operations on the locked row COMMIT;

2. Table-level locking using LOCK TABLES:

You can use LOCK TABLES to lock one or more tables in a database. The following example shows how to lock the 'users' table:

LOCK TABLES users WRITE; -- perform some operations on the locked table UNLOCK TABLES;

Note that you must release the lock using UNLOCK TABLES when you are finished with the locked tables.

3. Database-level locking using FLUSH TABLES WITH READ LOCK:

You can use FLUSH TABLES WITH READ LOCK to lock the entire database for read-only access. The following example shows how to lock the entire database:

FLUSH TABLES WITH READ LOCK; -- perform some read-only operations on the locked database UNLOCK TABLES;

Note that you must release the lock using UNLOCK TABLES when you are finished with the locked database.

4. Pessimistic locking using transactions:

You can use transactions to implement pessimistic locking. The following example shows how to lock the 'users' table for write access:

BEGIN; SELECT * FROM users WHERE id = 1 FOR UPDATE; -- perform some operations on the locked row COMMIT;

Note that you must commit or rollback the transaction to release the lock.

5. Optimistic locking using versioning:

You can use versioning to implement optimistic locking. The following example shows how to add a version column to the 'users' table:

ALTER TABLE users ADD COLUMN version INT NOT NULL DEFAULT 0;

You can then use the version column to detect and prevent concurrent updates to a row. The following example shows how to update the 'users' table using the version column:

UPDATE users SET name = 'John', version = version + 1 WHERE id = 1 AND version = 1;

Note that you must check the version column before updating the row to ensure that no other transaction has updated the row since the last read.