mirror of https://github.com/postgres/postgres
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installations whose pg_config program does not appear first in the PATH. Per gripe from Eddie Stanley and subsequent discussions with Fabien Coelho and others. |
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README.uuid-ossp
UUID Generation Functions ========================= Peter Eisentraut <peter_e@gmx.net> This module provides functions to generate universally unique identifiers (UUIDs) using one of the several standard algorithms, as well as functions to produce certain special UUID constants. Installation ------------ The extra library required can be found at <http://www.ossp.org/pkg/lib/uuid/>. UUID Generation --------------- The relevant standards ITU-T Rec. X.667, ISO/IEC 9834-8:2005, and RFC 4122 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. uuid_generate_v1() ~~~~~~~~~~~~~~~~~~ This function 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() ~~~~~~~~~~~~~~~~~~~~ This function generates a version 1 UUID but uses a random multicast MAC address instead of the real MAC address of the computer. uuid_generate_v3(namespace uuid, name text) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ This function 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 below. (It could be any UUID in theory.) The name is an identifier in the selected namespace. For example: 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() ~~~~~~~~~~~~~~~~~~ This function generates a version 4 UUID, which is derived entirely from random numbers. uuid_generate_v5(namespace uuid, name text) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ This function 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. UUID Constants -------------- uuid_nil() A "nil" UUID constant, which does not occur as a real UUID. uuid_ns_dns() Constant designating the DNS namespace for UUIDs. uuid_ns_url() Constant designating the URL namespace for UUIDs. uuid_ns_oid() Constant designating the ISO object identifier (OID) namespace for UUIDs. (This pertains to ASN.1 OIDs, unrelated to the OIDs used in PostgreSQL.) uuid_ns_x500() Constant designating the X.500 distinguished name (DN) namespace for UUIDs.