Is UUID really unique?

Is UUID really unique? A UUID (Universal Unique Identifier) is a 128-bit value used to uniquely identify an object or entity on the internet. Depending on the specific mechanisms used, a UUID is either guaranteed to be different or is, at least, extremely likely to be different from any other UUID generated until A.D. 3400.

What is difference between GUID and UUID? In general, there is no difference between a GUID and UUID. Both are 128 bit identifiers. UUID is defined via IETF RFC4122 whereas GUID was defined by Microsoft for the Windows O/S.

Is UUID same as UDID? UUID: Universal unique identifier, Which is used to identify anything on the internet uniquely. Each app on iPhone has its own UUID. UDID: Unique Device Identifier is used to identify the device uniquely. Usually it is used for registration for remote notifications, Installation and so on.

How do I decode a GUID? To determine the variant you look at the bits of the 17th hex digit in a UUID. For example, if the 4 binary digits begin “10” then the variant is “DCE 1.1, ISO/IEC 11578:1996”. If the binary digits begin “110” then the UUID is a “Microsoft GUID”.

Is UUID really unique? – Additional Questions


Is UUID a string?

The UUID as a 16-byte string (containing the six integer fields in big-endian byte order).

How many digits is a GUID?

A GUID is a 128-bit value consisting of one group of 8 hexadecimal digits, followed by three groups of 4 hexadecimal digits each, followed by one group of 12 hexadecimal digits. The following example GUID shows the groupings of hexadecimal digits in a GUID: 6B29FC40-CA47-1067-B31D-00DD010662DA.

Is a GUID a hash?

You can see why programmers use GUIDs as unique identifiers. It would take billions upon billions of years to generate two GUIDs that are the same. A hash is a value that is calculated by running some data (like a GUID) through an algorithm, which produces a checksum (kind of like a digital fingerprint).

Can a GUID be duplicated?

How unique is a GUID? 128-bits is big enough and the generation algorithm is unique enough that if 1,000,000,000 GUIDs per second were generated for 1 year the probability of a duplicate would be only 50%. Or if every human on Earth generated 600,000,000 GUIDs there would only be a 50% probability of a duplicate.

What is the GUID format?

The GUID data type is a text string representing a Class identifier (ID). COM must be able to convert the string to a valid Class ID. All GUIDs must be authored in uppercase. The valid format for a GUID is {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX} where X is a hex digit (0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F).

What is GUID value?

The globally unique identifier (GUID) data type in SQL Server is represented by the uniqueidentifier data type, which stores a 16-byte binary value. A GUID is a binary number, and its main use is as an identifier that must be unique in a network that has many computers at many sites.

Should I use a GUID?

Use guids when you have multiple independent systems or clients generating ID’s that need to be unique. For example, if I have 5 client apps creating and inserting transactional data into a table that has a unique constraint on the ID, then use guids.

Is GUID a string?

A GUID is a 16-byte (128-bit) number, typically represented by a 32-character hexadecimal string.

What is GUID used for?

A GUID (globally unique identifier) is a 128-bit text string that represents an identification (ID). Organizations generate GUIDs when a unique reference number is needed to identify information on a computer or network. A GUID can be used to ID hardware, software, accounts, documents and other items.

How many bytes is a GUID?

A GUID is a 128-bit integer (16 bytes) that can be used across all computers and networks wherever a unique identifier is required.

How is a GUID generated?

Basically, a a GUID is generated using a combination of: The MAC address of the machine used to generate the GUID (so GUIDs generated on different machines are unique unless MAC addresses are re-used) Timestamp (so GUIDs generated at different times on the same machine are unique)

Can GUID be primary key?

GUIDs can be considered as global primary keys. Local primary keys are used to uniquely identify records within a table. On the other hand, GUIDs can be used to uniquely identify records across tables, databases, and servers.

Should I use GUID or int?

An INT is certainly much easier to read when debugging, and much smaller. I would, however, use a GUID or similar as a license key for a product. You know it’s going to be unique, and you know that it’s not going to be sequential.

What datatype is GUID?

The GUID data type is a 16 byte binary data type. This data type is used for the global identification of objects, programs, records, and so on. The important property of a GUID is that each value is globally unique.

Can you index a GUID?

As GUIDs are randomly generated, defining the clustered index on the GUID column will lead to page splits in the page structure where data is entered in the middle of the page based on the value of the uniqueidentifier. This type of page split will have an impact on INSERTs and UPDATEs.

Is primary key always clustered index?

The primary key is the default clustered index in SQL Server and MySQL. This implies a ‘clustered index penalty’ on all non-clustered indexes.