uuid-ossp
=========

uuid-ossp

The `uuid-ossp` module provides functions to generate universally unique
identifiers (UUIDs) using one of several standard algorithms. There are
also functions to produce certain special UUID constants. This module is
only necessary for special requirements beyond what is available in core
PostgreSQL. See [???](#functions-uuid) for built-in ways to generate
UUIDs.

This module is considered "trusted", that is, it can be installed by
non-superusers who have `CREATE` privilege on the current database.

`uuid-ossp` Functions
---------------------

[table\_title](#uuid-ossp-functions) shows the functions available to
generate UUIDs. The relevant standards ITU-T Rec. X.667, ISO/IEC
9834-8:2005, and [RFC 4122](https://tools.ietf.org/html/rfc4122) specify
four algorithms for generating UUIDs, identified by the version numbers
1, 3, 4, and 5. (There is no version 2 algorithm.) Each of these
algorithms could be suitable for a different set of applications.

+-----------------------------------------------------------------------+
| Function                                                              |
|                                                                       |
| Description                                                           |
+=======================================================================+
| uuid\_generate\_v1 `uuid_generate_v1` () uuid                         |
|                                                                       |
| Generates a version 1 UUID. This involves the MAC address of the      |
| computer and a time stamp. Note that UUIDs of this kind reveal the    |
| identity of the computer that created the identifier and the time at  |
| which it did so, which might make it unsuitable for certain           |
| security-sensitive applications.                                      |
+-----------------------------------------------------------------------+
| uuid\_generate\_v1mc `uuid_generate_v1mc` () uuid                     |
|                                                                       |
| Generates a version 1 UUID, but uses a random multicast MAC address   |
| instead of the real MAC address of the computer.                      |
+-----------------------------------------------------------------------+
| uuid\_generate\_v3 `uuid_generate_v3` ( `namespace` `uuid`, `name`    |
| `text` ) uuid                                                         |
|                                                                       |
| Generates a version 3 UUID in the given namespace using the specified |
| input name. The namespace should be one of the special constants      |
| produced by the `uuid_ns_*()` functions shown in                      |
| [table\_title](#uuid-ossp-constants). (It could be any UUID in        |
| theory.) The name is an identifier in the selected namespace.         |
|                                                                       |
| For example:                                                          |
|                                                                       |
|     SELECT uuid_generate_v3(uuid_ns_url(), 'http://www.postgresql.org |
| ');                                                                   |
|                                                                       |
| The name parameter will be MD5-hashed, so the cleartext cannot be     |
| derived from the generated UUID. The generation of UUIDs by this      |
| method has no random or environment-dependent element and is          |
| therefore reproducible.                                               |
+-----------------------------------------------------------------------+
| `uuid_generate_v4` () uuid                                            |
|                                                                       |
| Generates a version 4 UUID, which is derived entirely from random     |
| numbers.                                                              |
+-----------------------------------------------------------------------+
| `uuid_generate_v5` ( `namespace` `uuid`, `name` `text` ) uuid         |
|                                                                       |
| Generates a version 5 UUID, which works like a version 3 UUID except  |
| that SHA-1 is used as a hashing method. Version 5 should be preferred |
| over version 3 because SHA-1 is thought to be more secure than MD5.   |
+-----------------------------------------------------------------------+

: Functions for UUID Generation

+-----------------------------------------------------------------------+
| Function                                                              |
|                                                                       |
| Description                                                           |
+=======================================================================+
| `uuid_nil` () uuid                                                    |
|                                                                       |
| Returns a "nil" UUID constant, which does not occur as a real UUID.   |
+-----------------------------------------------------------------------+
| `uuid_ns_dns` () uuid                                                 |
|                                                                       |
| Returns a constant designating the DNS namespace for UUIDs.           |
+-----------------------------------------------------------------------+
| `uuid_ns_url` () uuid                                                 |
|                                                                       |
| Returns a constant designating the URL namespace for UUIDs.           |
+-----------------------------------------------------------------------+
| `uuid_ns_oid` () uuid                                                 |
|                                                                       |
| Returns a constant designating the ISO object identifier (OID)        |
| namespace for UUIDs. (This pertains to ASN.1 OIDs, which are          |
| unrelated to the OIDs used in PostgreSQL.)                            |
+-----------------------------------------------------------------------+
| `uuid_ns_x500` () uuid                                                |
|                                                                       |
| Returns a constant designating the X.500 distinguished name (DN)      |
| namespace for UUIDs.                                                  |
+-----------------------------------------------------------------------+

: Functions Returning UUID Constants

Building `uuid-ossp`
--------------------

Historically this module depended on the OSSP UUID library, which
accounts for the module\'s name. While the OSSP UUID library can still
be found at [](http://www.ossp.org/pkg/lib/uuid/), it is not well
maintained, and is becoming increasingly difficult to port to newer
platforms. `uuid-ossp` can now be built without the OSSP library on some
platforms. On FreeBSD, NetBSD, and some other BSD-derived platforms,
suitable UUID creation functions are included in the core `libc`
library. On Linux, macOS, and some other platforms, suitable functions
are provided in the `libuuid` library, which originally came from the
`e2fsprogs` project (though on modern Linux it is considered part of
`util-linux-ng`). When invoking `configure`, specify `--with-uuid=bsd`
to use the BSD functions, or `--with-uuid=e2fs` to use `e2fsprogs`\'
`libuuid`, or `--with-uuid=ossp` to use the OSSP UUID library. More than
one of these libraries might be available on a particular machine, so
`configure` does not automatically choose one.

Author
------

Peter Eisentraut <peter_e@gmx.net>
