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. On Linux, OS X, 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). On FreeBSD, NetBSD, and some other BSD-derived platforms, suitable UUID creation functions are included in the core libc library. uuid-ossp can now be built without the OSSP library on some platforms. While the OSSP UUID library can still be found at, it is not well maintained, and is becoming increasingly difficult to port to newer platforms.
Historically this module depended on the OSSP UUID library, which accounts for the module's name. Version 5 should be preferred over version 3 because SHA-1 is thought to be more secure than MD5. This function generates a version 5 UUID, which works like a version 3 UUID except that SHA-1 is used as a hashing method. Uuid_generate_v5(namespace uuid, name text) This function generates a version 4 UUID, which is derived entirely from random numbers. The generation of UUIDs by this method has no random or environment-dependent element and is therefore reproducible. The name parameter will be MD5-hashed, so the cleartext cannot be derived from the generated UUID.
(It could be any UUID in theory.) The name is an identifier in the selected namespace.įor example: SELECT uuid_generate_v3(uuid_ns_url(), '') The namespace should be one of the special constants produced by the uuid_ns_*() functions shown in Table F-34. This function generates a version 3 UUID in the given namespace using the specified input name. Uuid_generate_v3(namespace uuid, name text)
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This function generates a version 1 UUID but uses a random multicast MAC address instead of the real MAC address of the computer. 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. This involves the MAC address of the computer and a time stamp. This function generates a version 1 UUID. Putting it all together this would look something like this: byte bytes = ncatenate(toByteArray(new UUID(0L, 0L)), "this is a test".getBytes(StandardCharsets.UTF_8)) In this tutorial, we will dive deep into UUIDs with all their cons and pros. Rails 6 release fresh out of beta introduces a new feature in ActiveRecord that makes working with UUID primary keys more straightforward. It offers some non-obvious advantages compared to standard integer-based keys. To get the same output as with PostgreSQL you have to concatenate the the namespace bytes and the name bytes together yourself.įor namespace you have used uuid_nil() (all zeroes) which is new UUID(0L, 0L) in Java. UUID also known as GUID is an alternative primary key type for SQL databases. The Java method nameUUIDFromBytes(byte name) takes only the name and hashes it with MD5 to create the UUID. The postgres function signature is uuid_generate_v3(namespace uuid, name text) so it takes the namespace UUID and name as arguments. Convert the resulting UUID to local byte order.Change certain bytes of the to predefined values (see link above).Compute the hash of the name space ID concatenated with the name.Convert the name to a canonical sequence of octets.Choose either MD5 or SHA-1 as the hash algorithm.Allocate a UUID to use as a "name space ID" for all UUIDs.The algorithm for generating a version 3 UUID is described here Though I must admit I have never tried the other way. SELECT uuidv3(textsend('this is a test')) Md5bytes := set_byte(md5bytes, 8, (get_byte(md5bytes, 8) & x'3F'::int)| x'80'::int) Īnd you should use internal textsend to convert text columns to bytea: md5Bytes |= 0x80 /* set to IETF variant */ md5Bytes |= 0x30 /* set to version 3 */ Though this is not an answer for the original question however I had to do this conversion in the other way around, that is, mimic UUID.nameUUIDFromBytes behaviour in PostgreSQL during a migration: CREATE EXTENSION IF NOT EXISTS "pgcrypto" ĬREATE EXTENSION IF NOT EXISTS "plpgsql" ĬREATE OR REPLACE FUNCTION uuidv3(bytes bytea)
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