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)
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    openGauss 2024-05-25 00:42:51
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