pg_locks

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

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_internal.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
virtualxid	text		Virtual ID of a transaction, or NULL if the object is not a virtual transaction ID
transactionid	xid		ID of a transaction, or NULL if the object is not a transaction ID
classid	oid	pg_class_internal.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
virtualtransaction	text		Virtual 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.
fastpath	boolean		True if lock was taken via fastpath, false if lock is taken via main lock table.
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 OushuDB segment id (dbid) where the lock is held.