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Aug 17, 2026 · Databases

Does Adding an Index Lock the Table? JD Interview Deep Dive (Full Score Edition)

The article explains that whether adding an index locks a MySQL table depends on the version and DDL algorithm—MySQL 5.5 and earlier lock the whole table, 5.6‑5.7 use Online DDL with brief metadata locks, and 8.0+ can create secondary indexes instantly without locking, while primary, unique, and full‑text indexes always require locking.