![]() ![]() ![]() This identifier is unique not only to the server on which it originated, but is unique across all servers in a given replication topology. Sequential UUIDs are a compromise - giving away a small amount of collision protection in order to gain what could be a significant efficiency boost in some circumstances (DB indexes being the main one). A global transaction identifier (GTID) is a unique identifier created and associated with each transaction committed on the server of origin (the source). UUIDs, including those that increment from the start point, are intended not to collide with those generated elsewhere. Well organized and easy to understand Web building tutorials with lots of examples of how to use HTML, CSS, JavaScript, SQL, Python, PHP, Bootstrap, Java. UUID() This function returns a Universal Unique Identifier (UUID), a 128-bit number composed of five hexadecimal numbers. > If you need something sequential then just use a much more simple number* You don't want to use sequential UUIDs in place of v4 UUIDs where security matters, or course, as it is easy to work the next in sequence. Is it possible to generate a UUID version 4 (completely random) in MySQL I would like to use it as a primary key. These are "atoms in several galaxies" level numbers. For most systems the chance of collision with sequential UUIDs is, while larger than with other types, still so small as to be inconsequential. Even if your system is up long enough to use 2^58 (2.88 10^17 if you want that in decimal) IDs generated this way, you still effectively have 64-bits of randomness even if the variant bits are present. If cryptographically secure randomness is required, the RandomRandomizer may be used with the RandomEngineSecure engine. Assuming the variant indicators are present, there is are 122 random bits. This function does not generate cryptographically secure values, and must not be used for cryptographic purposes, or purposes that require returned values to be unguessable. MS SQL Server's NEWSEQUENTIALID function returns something akin to a v4 UUID (fully random, aside from variant indicator bits, I'm not sure if the variant bits are respected in NEWSEQUENTIALIDs output or if it just returns a 128-bit number) but after the first is generated the rest follow in sequence until the sequence is reset (by a reboot). IIRC this is often a mix of hardware network address and a portion that is either random or based on a high-precision time, so it is still unlikely that you'll see collisions between machines. It depends on how the non-sequential part is derived. ![]()
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