> [!NOTE] LockRows > <table> > <tr> > <td width="25%"><img src="assets/ex_lockrows.png"></td> > <td>Implements <code>FOR UPDATE</code> or <code>FOR SHARE</code> locking. This node ensures that the rows returned by the query are locked against concurrent modification until the current transaction commits or rolls back.</td> > </tr> > </table> > > ```sql > -- Locking a specific row for modification > EXPLAIN (ANALYZE, COSTS, BUFFERS, VERBOSE) > SELECT * FROM animals WHERE id = 1 FOR UPDATE; > ``` > > ```text > LockRows (cost=1.29..9.31 rows=1 width=33) (actual time=1.017..1.017 rows=1 loops=1) > Output: id, name, species_id, created_at, ctid > Buffers: shared hit=5 dirtied=1 > -> Index Scan using animals_pkey on public.animals (...) > ``` > > <table> > <tr> > <td rowspan="5" width="25%"><img src="assets/ex_lock_rows.svg"></td> > <td><b>Performance</b></td><td>Introduces overhead for lock acquisition and can lead to transaction blocking if other sessions held conflicting locks.</td> > </tr> > <tr><td><b>Factors</b></td><td>Number of rows locked and the degree of lock contention.</td></tr> > <tr><td><b>Cost</b></td><td><code>lock acquisition cost * number of rows</code></td></tr> > <tr><td><b>Operates on</b></td><td><a href="Structures/Tuple">Tuple</a></td></tr> > <tr><td><b>Workloads</b></td><td><a href="Workloads/Lock/Lock/Lock_Tuple">Lock: Tuple</a>, <a href="Workloads/Lock/Lock/Lock_TransactionId">Lock: TransactionId</a>, <a href="Workloads/LWLock/Lock/LockManager">LWLock: LockManager</a>, <a href="Workloads/IPC/Snapshot/SafeSnapshot">IPC: SafeSnapshot</a></td></tr> > <tr><td colspan="3"><b>Description</b>: Locks rows without changing them.</td></tr> > </table>