</para>

<para>

When the <structname>pg_locks</structname> view is accessed, the

internal lock manager data structures are momentarily locked, and

a copy is made for the view to display. This ensures that the

view produces a consistent set of results, while not blocking

normal lock manager operations longer than necessary. Nonetheless

there could be some impact on database performance if this view is

frequently accessed.

The <structname>pg_locks</structname> view displays data from both the

regular lock manager and the predicate lock manager, which are

separate systems. When this view is accessed, the internal data

structures of each lock manager are momentarily locked, and copies are

made for the view to display. Each lock manager will therefore

produce a consistent set of results, but as we do not lock both lock

managers simultaneously, it is possible for locks to be taken or

released after we interrogate the regular lock manager and before we

interrogate the predicate lock manager. Each lock manager is only

locked for the minimum possible time so as to reduce the performance

impact of querying this view, but there could nevertheless be some

impact on database performance if it is frequently accessed.

</para>

<para>