AWS Certified Data Engineer Associate DEA-C01 Practice Question

An AWS Lambda function that runs every hour recalculates summary tables in an Amazon RDS for MySQL 8.0 database. Occasionally, two invocations overlap, resulting in duplicate updates and deadlocks. You need to guarantee that only one invocation performs the recalculation at any given time while ordinary read traffic to the tables continues uninterrupted. Which solution meets the requirement with the least code and configuration changes?

Change the summary table to the MyISAM engine and issue LOCK TABLES WRITE before updates and UNLOCK TABLES afterward.
Call the MySQL functions GET_LOCK('recalc', timeout) at the start of the job and RELEASE_LOCK('recalc') when it finishes.
Set the innodb_table_locks parameter to ON in the DB parameter group so InnoDB automatically applies a global table lock during the transaction.
Enable Multi-AZ for the RDS instance so the standby blocks concurrent write attempts during the recalculation window.

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Answer Description

The built-in MySQL function GET_LOCK obtains a user-defined named lock that is held by the current session until it explicitly calls RELEASE_LOCK or the session ends. If another Lambda invocation tries to acquire the same named lock, it blocks (or times out) until the lock is free, preventing concurrent execution of the recalculation code. Because the lock is advisory and scoped only to sessions requesting it, other client sessions can continue to read from the tables without waiting. Simply adding GET_LOCK at the start of the job and RELEASE_LOCK at the end meets the requirement with minimal changes.

Enabling innodb_table_locks does not serialize application-level tasks; it only affects how metadata locks are recorded. Converting the table to MyISAM and issuing LOCK TABLES would block all reads during the job and requires an engine change that is not recommended for RDS MySQL 8.0. Multi-AZ deployment improves availability but does nothing to prevent concurrent Lambda invocations from running against the primary instance.

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