Editing Two-phase locking (section)

===Two-phase locking===
According to the '''two-phase locking''' protocol, each transaction handles its locks in two distinct, consecutive phases during the transaction's execution:

# '''Expanding phase''' (aka Growing phase): locks are acquired and no locks are released (the number of locks can only increase).
# '''Shrinking phase''' (aka Contracting phase): locks are released and no locks are acquired.

The two phase locking rules can be summarized as: each transaction must never acquire a lock after it has released a lock. The [[serializability]] property is guaranteed for a schedule with transactions that obey this rule.

Typically, without explicit knowledge in a transaction on end of phase 1, the rule is safely determined only when a transaction has completed processing and requested commit. In this case, all the locks can be released at once (phase 2).