Object Identifier Types

Object identifiers (OIDs) are used internally by openGauss as primary keys for various system catalogs. OIDs are not added to user-created tables by the system. The OID type represents an object identifier.

The OID type is currently implemented as an unsigned four-byte integer. So, using a user-created table's OID column as a primary key is discouraged.

Table 1 Object identifier types

Name	Reference	Description	Example
OID	N/A	Numeric object identifier	564182
CID	N/A	A command identifier. This is the data type of the system columns cmin and cmax. Command identifiers are 32-bit quantities.	N/A
XID	N/A	A transaction identifier. This is the data type of the system columns xmin and xmax. Transaction identifiers are also 32-bit quantities.	N/A
TID	N/A	A row identifier. This is the data type of the system column ctid. A row ID is a pair (block number, tuple index within block) that identifies the physical location of the row within its table.	N/A
REGCONFIG	pg_ts_config	Text search configuration	english
REGDICTIONARY	pg_ts_dict	Text search dictionary	simple
REGOPER	pg_operator	Operator name	-
REGOPERATOR	pg_operator	Operator with argument types	*(integer,integer) or -(NONE,integer)
REGPROC	pg_proc	Function name	sum
REGPROCEDURE	pg_proc	Function with argument types	sum(int4)
REGCLASS	pg_class	Relation name	pg_type
REGTYPE	pg_type	Data type name	integer

The OID type is used for a column in the database system catalog.

Example:

postgres=# SELECT oid FROM pg_class WHERE relname = 'pg_type';
 oid  
------
 1247
(1 row)

The alias type for OID is REGCLASS which allows simplified search for OID values.

Example:

postgres=# SELECT attrelid,attname,atttypid,attstattarget FROM pg_attribute WHERE attrelid = 'pg_type'::REGCLASS;
 attrelid |  attname   | atttypid | attstattarget 
----------+------------+----------+---------------
     1247 | xc_node_id     |       23 |             0
     1247 | tableoid       |       26 |             0
     1247 | cmax           |       29 |             0
     1247 | xmax           |       28 |             0
     1247 | cmin           |       29 |             0
     1247 | xmin           |       28 |             0
     1247 | oid            |       26 |             0
     1247 | ctid           |       27 |             0
     1247 | typname        |       19 |            -1
     1247 | typnamespace   |       26 |            -1
     1247 | typowner       |       26 |            -1
     1247 | typlen         |       21 |            -1
     1247 | typbyval       |       16 |            -1
     1247 | typtype        |       18 |            -1
     1247 | typcategory    |       18 |            -1
     1247 | typispreferred |       16 |            -1
     1247 | typisdefined   |       16 |            -1
     1247 | typdelim       |       18 |            -1
     1247 | typrelid       |       26 |            -1
     1247 | typelem        |       26 |            -1
     1247 | typarray       |       26 |            -1
     1247 | typinput       |       24 |            -1
     1247 | typoutput      |       24 |            -1
     1247 | typreceive     |       24 |            -1
     1247 | typsend        |       24 |            -1
     1247 | typmodin       |       24 |            -1
     1247 | typmodout      |       24 |            -1
     1247 | typanalyze     |       24 |            -1
     1247 | typalign       |       18 |            -1
     1247 | typstorage     |       18 |            -1
     1247 | typnotnull     |       16 |            -1
     1247 | typbasetype    |       26 |            -1
     1247 | typtypmod      |       23 |            -1
     1247 | typndims       |       23 |            -1
     1247 | typcollation   |       26 |            -1
     1247 | typdefaultbin  |      194 |            -1
     1247 | typdefault     |       25 |            -1
     1247 | typacl         |     1034 |            -1
(38 rows)