How Can I Perform an ALTER TABLE Operation in MySQL Without Locking the Entire Table?

ALTER TABLE without Locking the Table

In the realm of database management, ALTER TABLE operations in MySQL typically inflict a table-level read-lock, impeding concurrent writes while allowing concurrent reads. For extensive tables, this can cause significant delays for INSERT or UPDATE statements.

One potential solution, though, is to consider a "hot alter" approach. While MySQL does not natively support this, other RDBMS systems may offer it. For MySQL, however, one must resort to a manual workaround:

• Establish a new table, mirroring the original table's structure, but with the desired additional column.
• Gradually transfer data in chunks from the original table to the new table, taking precautionary measures to handle any simultaneous INSERT/UPDATE/DELETE operations on the original table (e.g., using triggers).
• Upon completion, swap the table names for the original and the new tables, preferably within a transaction.
• Reconfigure any stored procedures that rely on the altered table.

It's important to note that adding a new column is inherently a transformative operation that impacts the entire table's structure and data organization on disk. Thus, this process unavoidably incurs a performance hit, analogous to an all-encompassing UPDATE operation. However, this workaround eliminates the need for explicit table locking, enabling data updates during the alteration process.

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