pg_locks

pg_locks

The pg_locks view provides access to information about the locks held by open transactions within Greenplum Database.

pg_locks contains one row per active lockable object, requested lock mode, and relevant transaction. Thus, the same lockable object may appear many times, if multiple transactions are holding or waiting for locks on it. However, an object that currently has no locks on it will not appear at all.

There are several distinct types of lockable objects: whole relations (such as tables), individual pages of relations, individual tuples of relations, transaction IDs, and general database objects. Also, the right to extend a relation is represented as a separate lockable object.

Table 1. pg_catalog.pg_locks
column type references description
locktype text   Type of the lockable object: relation, extend, page, tuple, transactionid, object, userlock, resource queue, or advisory
database oid pg_database.oid OID of the database in which the object exists, zero if the object is a shared object, or NULL if the object is a transaction ID
relation oid pg_class.oid OID of the relation, or NULL if the object is not a relation or part of a relation
page integer   Page number within the relation, or NULL if the object is not a tuple or relation page
tuple smallint   Tuple number within the page, or NULL if the object is not a tuple
transactionid xid   ID of a transaction, or NULL if the object is not a transaction ID
classid oid pg_class.oid OID of the system catalog containing the object, or NULL if the object is not a general database object
objid oid any OID column OID of the object within its system catalog, or NULL if the object is not a general database object
objsubid smallint   For a table column, this is the column number (the classid and objid refer to the table itself). For all other object types, this column is zero. NULL if the object is not a general database object
transaction xid   ID of the transaction that is holding or awaiting this lock
pid integer   Process ID of the server process holding or awaiting this lock. NULL if the lock is held by a prepared transaction
mode text   Name of the lock mode held or desired by this process
granted boolean   True if lock is held, false if lock is awaited.
mppsessionid integer   The id of the client session associated with this lock.
mppiswriter boolean   Specifies whether the lock is held by a writer process.
gp_segment_id integer   The Greenplum segment id (dbid) where the lock is held.