Merge pull request #23873 from abpframework/article-sequential-guids

Add article on generating sequential GUIDs in .NET

Author: EngincanV

docs/en/Community-Articles/2025-10-03-Generating-Sequential-GUIDs/Post.md

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+# You May Have Trouble with GUIDs: Generating Sequential GUIDs in .NET
+
+
+If you’ve ever shoved a bunch of `Guid.NewGuid()` values into a SQL Server table with a clustered index on the PK, you’ve probably felt the pain: **Index fragmentation so bad you could use it as modern art.** Inserts slow down, page splits go wild, and your DBA starts sending you passive-aggressive Slack messages.
+
+And yet… we keep doing it. Why? Because GUIDs are _easy_. They’re globally unique, they don’t need a round trip to the DB, and they make distributed systems happy. But here’s the catch: **random GUIDs are absolute chaos for ordered indexes**.
+
+## The Problem with Vanilla GUIDs
+
+* **Randomness kills order** — clustered indexes thrive on sequential inserts; random GUIDs force constant reordering.
+
+* **Performance hit** — every insert can trigger page splits and index reshuffling.
+
+* **Storage bloat** — fragmentation means wasted space and slower reads.
+
+Sure, you could switch to int or long identity columns, but then you lose the distributed generation magic and security benefits (predictable IDs are guessable).
+
+## Sequential GUIDs to the Rescue
+
+Sequential GUIDs keep the uniqueness but add a predictable ordering component, usually by embedding a timestamp in part of the GUID. This means:
+
+* Inserts happen at the “end” of the index, not all over the place.
+
+* Fragmentation drops dramatically.
+
+* You still get globally unique IDs without DB trips.
+
+Think of it as **GUIDs with manners**.
+
+## ABP Framework’s Secret Sauce
+
+
+Here’s where ABP Framework flexes: it **uses sequential GUIDs by default** for entity IDs. No ceremony, no “remember to call this helper method”, it’s baked in.
+
+Under the hood:
+
+* ABP ships with IGuidGenerator (default: SequentialGuidGenerator).
+
+* It picks the right sequential strategy for your DB provider:
+  
+  * **SequentialAtEnd** → SQL Server
+  
+  * **SequentialAsString** → MySQL/PostgreSQL
+  
+  * **SequentialAsBinary** → Oracle
+
+* EF Core integration packages auto-configure this, so you rarely need to touch it.
+
+Example in ABP:
+
+```csharp
+public class MyProductService : ITransientDependency
+{
+    private readonly IRepository<Product, Guid> _productRepository;
+    private readonly IGuidGenerator _guidGenerator;
+
+
+    public MyProductService(
+        IRepository<Product, Guid> productRepository,
+        IGuidGenerator guidGenerator)
+    {
+        _productRepository = productRepository;
+        _guidGenerator = guidGenerator;
+    }
+
+
+    public async Task CreateAsync(string productName)
+    {
+        var product = new Product(_guidGenerator.Create(), productName);
+        await _productRepository.InsertAsync(product);
+    }
+}
+```
+
+No `Guid.NewGuid()` here, `_guidGenerator.Create()` gives you a sequential GUID every time.
+
+## Benefits of Sequential GUIDs
+
+Let’s say you’re inserting 1M rows into a table with a clustered primary key:
+
+* **Random GUIDs** → fragmentation ~99%, insert throughput tanks.
+
+* **Sequential GUIDs** → fragmentation stays low, inserts fly.
+
+In high-volume systems, this difference is **not** academic, it’s the difference between smooth scaling and spending weekends rebuilding indexes.
+
+## When to Use Sequential GUIDs
+
+* **Distributed systems** that still want DB-friendly inserts.
+
+* **High-write workloads** with clustered indexes on GUID PKs.
+
+* **Multi-tenant apps** where IDs need to be unique across tenants.
+
+## When Random GUIDs Still Make Sense
+
+* Security through obscurity, if you don’t want IDs to hint at creation order.
+
+* Non-indexed identifiers, fragmentation isn’t a concern.
+
+## The Final Take
+
+ABP’s default sequential GUID generation is one of those “**small but huge**” features. It’s the kind of thing you don’t notice until you benchmark, and then you wonder why you ever lived without it.
+
+## Links
+You may want to check the following references to learn more about sequential GUIDs:
+
+- [ABP Framework Documentation: Sequential GUIDs](https://docs.abp.io/en/abp/latest/Guid-Generation)