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MySQL + SQL · Lesson 87

Locks and Deadlocks in MySQL

Locks

A lock reserves a row or table for one transaction so others wait, preventing conflicting changes.
  • Shared (read) lock — others can read, not write.
  • Exclusive (write) lock — others cannot read or write.

Deadlock

A deadlock happens when two transactions each wait for a row the other holds — neither can proceed. MySQL detects this and automatically rolls back one transaction.

Avoiding Deadlocks

  • Access tables/rows in the same order in every transaction.
  • Keep transactions short.

Summary

  • Locks reserve rows; shared = read, exclusive = write.
  • A deadlock is mutual waiting; MySQL rolls back one to break it.
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