How Can I Execute MySQL SELECT Queries Without Locking?

Can MySQL Queries Be Executed Without Inducing Locking?

In MySQL, queries such as SELECT COUNT(online.account_id) cnt from online can inadvertently cause database locks, especially when tables like online are subject to frequent modifications by external events. To mitigate this issue, it is important to understand if MySQL offers any mechanisms to execute select statements without triggering locks.

One potential solution is to employ the READ-UNCOMMITTED transaction isolation level. However, this approach may not be compatible with slave database configurations, as it can lead to binary logging errors.

An alternative technique is to utilize the SET command to temporarily adjust the transaction isolation level to READ UNCOMMITTED, execute the select statement, and then reset the isolation level back to REPEATABLE READ. This method can be effectively implemented as follows:

SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED ;
SELECT * FROM TABLE_NAME ;
SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ ;

For slave databases, a more appropriate approach is to utilize the COMMIT command instead of the SET command to revert the isolation level after the select statement has executed. This can be achieved by employing the following sequence:

SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED ;
SELECT * FROM TABLE_NAME ;
COMMIT ;

By incorporating these techniques, MySQL users can execute select statements without inducing locks, effectively addressing the issue outlined in the original query.

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