PG_CLASS

PG_CLASS records database objects and their relationship.

Table 1 PG_CLASS columns

Name	Type	Description
oid	oid	Row identifier (hidden attribute, which must be specified)
relname	name	Name of an object, such as a table, index, or view
relnamespace	oid	OID of the namespace that contains the relationship
reltype	oid	Data type that corresponds to the table's row type. The index is 0 because the index does not have PG_TYPE records.
reloftype	oid	OID of the composite type (0 for other types)
relowner	oid	Owner of the relationship
relam	oid	Access method used, such as B-tree and hash, if this is an index
relfilenode	oid	Name of the on-disk file of this relationship (0 if such file does not exist)
reltablespace	oid	Tablespace in which this relationship is stored. If the value is 0, the default tablespace in this database is used. This column is meaningless if the relationship has no on-disk file.
relpages	double precision	Size of the on-disk representation of the table in pages (of size BLCKSZ). This is only an estimate used by the optimizer.
reltuples	double precision	Number of rows in the table. This is only an estimate used by the optimizer.
relallvisible	integer	Number of pages marked as all visible in the table. This column is used by the optimizer for optimizing SQL execution. It is updated by VACUUM, ANALYZE, and a few DDL statements such as CREATE INDEX.
reltoastrelid	oid	OID of the TOAST table associated with the table (0 if no TOAST table exists). The TOAST table stores large columns "offline" in a secondary table.
reltoastidxid	oid	OID of the index for a TOAST table (0 for a table other than a TOAST table)
reldeltarelid	oid	OID of a Delta table Delta tables are attached to column-store tables. They store long tail data generated during storage data import.
reldeltaidx	oid	OID of the index for a Delta table
relcudescrelid	oid	OID of a CU description table. CU description tables (Desc tables) belong to column-store tables. They control whether storage data in the HDFS table directory is visible.
relcudescidx	oid	OID of the index for a CU description table
relhasindex	Boolean	Its value is true if this column is a table and has (or recently had) at least one index. It is set by CREATE INDEX but is not immediately cleared by DROP INDEX. If the VACUUM process detects that a table has no index, it clears the relhasindex column and sets the value to false.
relisshared	Boolean	Its value is true if the table is shared across all database nodes in MogDB. Only certain system catalogs (such as PG_DATABASE) are shared.
relpersistence	"char"	- p: permanent table - u: non-log table - g: temporary table
relkind	"char"	- r: ordinary table - i: index - I: GLOBAL index of a partitioned table - s: sequence - v: view - c: composite type - t: TOAST table - f: foreign table
relnatts	smallint	Number of user columns in the relationship (excluding system columns). PG_ATTRIBUTE has the same number of rows as the user columns.
relchecks	smallint	Number of check constraints in the table. For details, see the system catalog PG_CONSTRAINT.
relhasoids	Boolean	Its value is true if an OID is generated for each row of the relationship.
relhaspkey	Boolean	Its value is true if the table has (or once had) a primary key.
relhasrules	Boolean	Its value is true if the table has rules. For details, see the system catalog PG_REWRITE.
relhastriggers	Boolean	The value is true if the table has (or once had) triggers. Triggers of the table and view are recorded in the system catalog PG_TRIGGER.
relhassubclass	Boolean	Its value is true if the table has (or once had) any inheritance child table.
relcmprs	tinyint	Whether the compression feature is enabled for the table. Note that only batch insertion triggers compression, so ordinary CRUD does not trigger compression. - 0: Tables that do not support compression (primarily system catalogs, on which the compression attribute cannot be modified). - 1: The compression feature of the table data is NOCOMPRESS or has no specified keyword. - 2: The compression feature of the table data is COMPRESS.
relhasclusterkey	Boolean	Whether the local cluster storage is used
relrowmovement	Boolean	Whether row migration is allowed when the partitioned table is updated. - true: Row migration is allowed. - false: Row migration is not allowed.
parttype	"char"	Whether the table or index has the property of a partitioned table. - p: The table or index has the property of a partitioned table. - n: The table or index does not have the property of a partitioned table. - v: The table is a value partitioned table in HDFS.
relfrozenxid	xid32	All transaction IDs before this one have been replaced with a permanent ("frozen") transaction ID in the table. This column is used to track whether the table needs to be vacuumed to prevent transaction ID wraparound (or to allow PG_CLOG to be shrunk). The value is 0 (InvalidTransactionId) if the relationship is not a table. To ensure forward compatibility, this column is reserved. The relfrozenxid64 column is added to record the information.
relacl	aclitem[]	Access permissions. The command output of the query is as follows: rolename=xxxx/yyyy - Assigning permissions to a role =xxxx/yyyy - Assigning the permission to public xxxx indicates assigned permissions, and yyyy indicates roles with the assigned permissions. For details on permission descriptions, see [Table 2](#Description of permissions).
relreplident	"char"	Identifier of a decoding column in logical decoding: - d: default (primary key, if any) - n: none - f: all columns - i: The indisreplident of the index is specified or the default index is used.
relfrozenxid64	xid	All transaction IDs before this one have been replaced with a permanent ("frozen") transaction ID in the table. This column is used to track whether the table needs to be vacuumed to prevent transaction ID wraparound (or to allow PG_CLOG to be shrunk). The value is 0 (InvalidTransactionId) if the relationship is not a table.
relbucket	oid	Bucket information in pg_hashbucket.
relbucketkey	int2vector	Column number of a hash partition.

Table 2 Description of permissions

Parameter	Parameter Description
r	SELECT (read)
w	UPDATE (write)
a	INSERT (insert)
d	DELETE
D	TRUNCATE
x	REFERENCES
t	TRIGGER
X	EXECUTE
U	USAGE
C	CREATE
c	CONNECT
T	TEMPORARY
A	ALTER
P	DROP
m	COMMENT
i	INDEX
v	VACUUM
*	Authorization options for preceding permissions