Guid Version 7 in .NET 9

Guid V4

The Guid type has been in .NET from the very beginning. You can create a new Guid with the NewGuid() method. 

var guid = Guid.NewGuid();

Console.WriteLine(guid);
// ee9d5db0-33cb-4408-ba9c-71289a823ba5

The NewGuid() method generates the GUID of version 4 following the UUID Version 4 specification in RFC 9562.

GUIDs are used in distributed systems. They ensure an ID is unique across multiple databases, servers, or systems. GUIDs are globally unique, so they’re perfect for scenarios where data might be merged from different sources or entities that need to be uniquely identified across distributed systems.

However, GUID v4 is not sequential, which can lead to significant index fragmentation in relational databases. When new rows are inserted, they will likely be placed in random positions within the index, leading to frequent page splits and a fragmented index. This fragmentation can degrade performance over time.

Entity Framework Core can generate sequential GUIDs. However, it has disadvantages. There are also NuGet packages for generating sequential GUIDs, such as SequentialGuid.

Guid V7

.NET 9 in preview 7 introduces a new GUID implementation based on timestamp and random. 

You can create a Guid using the CreateVersion7() method.

var guid7 = Guid.CreateVersion7();

Console.WriteLine(guid7);
// 01917ba0-a4b5-793b-a915-1caeceb5843e

Also, the Guid type has a new Version property, so you can check the version your GUID was created with.

Let’s compare the creation of five GUIDs of both versions. 

for (int i = 0; i < 5; i++)
{
    var guid = Guid.NewGuid();

    Console.WriteLine($"V{guid.Version}: {guid}");
}
Console.WriteLine();
for (int i = 0; i < 5; i++)
{
    var guid = Guid.CreateVersion7();

    Console.WriteLine($"V{guid.Version}: {guid}");
}

The output:

V4: 0557b321-abcf-4390-abee-4b8fbf93ff34
V4: 21a98165-af1e-477e-9dee-7eb9c79e6c77
V4: 7dbbf973-c55a-4917-87a5-95c16f356262
V4: b13892f2-334f-409a-b9de-d90dea21eed4
V4: 52dc44f7-76e0-4689-a5e6-1a0f1c5f37a3

V7: 01917bbe-d973-7beb-a813-106fcb4eff98
V7: 01917bbe-d973-703c-8365-b7596740ac82
V7: 01917bbe-d973-7234-a580-5f07730a3ad7
V7: 01917bbe-d973-7751-b8ba-bb73afab4a5d
V7: 01917bbe-d973-7d36-9be0-2e6317919153

You can see that GUID V7 is sequential, which makes it more suitable for relationship databases. 

You can also pass the DateTimeOffset when creating a new Guide to control TimeStamp. 

Guid.CreateVersion7(TimeProvider.System.GetUtcNow());