pg_locks

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

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. An object with no current locks on it will not appear in the view 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 (both virtual and permanent IDs), and general database objects. Also, the right to extend a relation is represented as a separate lockable object.

Column Type References Description

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, `0` 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
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.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 `0`. `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 the 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 content ID of the Greengage DB segment where the lock is held

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, 0 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

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.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 0. 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 the 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 content ID of the Greengage DB segment where the lock is held

pg_cursors

pg_matviews