Schema Changes in MySQL: Will Your Table Be Locked?

Table-level locking in MySQL can significantly impact the performance of business systems, especially for large datasets. When executing an ALTER TABLE operation, MySQL locks the table by default, blocking other transactions until the operation completes. This can cause query delays, blocked write operations, and system slowdowns. However, in newer versions of MySQL, adding a column to a table using the InnoDB storage engine may not necessarily lock the table. MySQL 5.6 introduced Online DDL operations, allowing certain table modifications to be performed without locking the table. In MySQL 5.6, adding a column is an online operation that can use ALGORITHM=INPLACE to avoid full table locking. MySQL 8.0 further optimized Online DDL operations, allowing most ALTER TABLE operations to be performed without locking the table. MySQL 8.0 introduces features like Atomic DDL, Instant Metadata Updates, and Incremental Metadata Updates to reduce table lock time and improve concurrent performance. Despite these optimizations, it's still recommended to perform ALTER TABLE operations during off-peak hours to minimize the impact on applications.