A shared table lock allows multiple transactions to read the data of a base table. A transaction that has a shared table lock on a base table can modify the table provided no other transaction holds a lock of any kind on the rows being modified.

A shared table lock is acquired, for example, by executing a LOCK TABLE...IN SHARED MODE statement. The REFRESH MATERIALIZED VIEW and REFRESH TEXT INDEX statements also provide a WITH SHARE MODE clause that you can use to create shared table locks on the underlying tables while the refresh operation takes place.

 See also