@dundich

In principle, it's great to extend the Outbox implementation to Postgres and thanks for taking the time.

I wonder if we truly need to provide that much PK flexibility which will bring in complexity to accommodate all the particulars:

• monotonically PK will likely require a call ahead of insert to the database to generate the number from a sequence - this will require an additional SQL call prior inserting the outbox row (I sense this is the case for Task<TOutboxKey> GenerateId())
• unless we could make it that the PK value can be deferred until insert is made, DB autoassigns PK value (from sequence) and value can be read directly after insert (one roundtrip)

Is there a strong need to avoid UUIDs/Guids for performance reasons and to prefer monotonically increasing PK (values generated by the DB)?
If this is the concern, my expectation is a small number of messages in the outbox (even in large message bursts), so I'm not entirely sure the performance of UUIDs/Guids is truly a major factor to consider. Messages in Outbox are regularly cleaned up too.

These are just my thoughts thinking out loud and perhaps I am missing something (have not worked with Postgress for a while).
Still it might make sense to extend the IOutboxRepository as you propose but we'd need to see how the end state implementation for Postgress outbox will look like and perhaps we limit PK flexibility.

Please let me know.

I am trying to solve the following infrastructure-specific problem.

A large number of messages and slow consumers overflow a bus with a limited size, so before sending I need to make sure that the bus is ready to receive messages.

Moreover, I need to hold all incoming messages for a long time - that's why partitions

As for generating an identifier and choosing a type for the key, the problem of "getting a timestamp from [ULID vs UUID7] and writing to a hot index area (when adding new records) + time-based partitions will be solved

At this stage it is still a draft and I am not sure about the correctness of the idea (It smells like Kafka in here.)

But I still think it's right to introduce a generator method for choosing a strategy (https://steven-giesel.com/blogPost/ea42a518-4d8b-4e08-8f73-e542bdd3b983)

public interface IOutboxRepository
{
    Task<Guid> GenerateId(CancellationToken cancellationToken);  // for client or database

IOutboxRepository<TOutboxKey> - causes an avalanche of changes and ULID not RFC, this ticket can be be closed + #312

Ok I understand now the use case. Let me look at the PR late today.

Guid is used in many databases, so the as generic type is probably overhead...

ps. The only thing missing is PKey control (want Genid).

@dundich I reviewed thePR #312 as well as the discussion in here.

This PR #312 causes a generics explosion that is dragged across many layers...

Here #314 is my quick proposal to allow flexible PKs, including preservation of existing Guids, but opening this up leveraging UUIDv7 capability (or other types) to achieve ordered PKs.

The key elements are:

• The OutboxMessage does not have any PK/ID property.
• GuidOutboxMessage is derived from the reduced OutboxMessage
• There is an interface IOutboxMessageAdapter with a default implementation of GuidOutboxMessageAdapter in the container
• To extend this for .NET9 UUIDv7, one has to provide IOutboxMessageAdapter implementation or derive from GuidOutboxMessageAdapter to use the new Guid.CreateVersion7();.
• This also opens up for the ability to use Int64 (or others) as PKs but it would need some more work to make the SQL migrations more extensible.

The PR is draft, few test need to be fixed.

Let me know your thoughts.

looks better but I have some comments, ... later

1. I'd add new interface ITimeResolver

https://andrewlock.net/exploring-the-dotnet-8-preview-avoiding-flaky-tests-with-timeprovider-and-itimer/?ref=grantwinney.com

// +
public interface ITimeResolver
{
    DateTime GetUtcNow();
}

public class TimeResolver : ITimeResolver
{
    public DateTime GetUtcNow() => DateTime.UtcNow;
}

// ~
public class GuidOutboxMessageAdapter(ITimeResolver timeResolver) : IOutboxMessageAdapter
{
    public OutboxMessage Create()
        => new GuidOutboxMessage
        {
            Id = Guid.NewGuid(),
            Timestamp = timeResolver.GetUtcNow() // <= ITimeResolver 
        };
// ....
}

// ~ this will affect the internal class OutboxSendingTask + 

// ~ init OutboxMessage
public abstract class OutboxMessage
{
    public DateTime Timestamp { get; set; }    // = DateTime.UtcNow;  no need

2. Performance IOutboxRepository (there's some testing to be done), LockAndWrite instead of LockAndSelect for ArrayPool

public interface IOutboxMessagePooler
{
    OutboxMessage[] Rent(int batchSize);
    void Return(OutboxMessage[] array);
}

public class OutboxMessagePooler: IOutboxMessagePooler
{
    public OutboxMessage[] Rent(int batchSize) => ArrayPool<OutboxMessage>.Shared.Rent(batchSize);
    public void Return(OutboxMessage[] array) => ArrayPool<OutboxMessage>.Shared.Return(array);
}

LockAndWrite instead of LockAndSelect

public interface IOutboxRepository
{
    Task<int> LockAndWrite(Memory<OutboxMessage> buffer, string instanceId, int batchSize, ... CancellationToken token);

~ class OutboxSendingTask.SendMessages

async internal Task<int> SendMessages(IServiceProvider serviceProvider, IOutboxRepository outboxRepository, CancellationToken cancellationToken)
 {
   //....
     do
     {
         
         int batchSize = _outboxSettings.PollBatchSize;
         var array = messagePooler.Rent(batchSize);  // <= 1
         try
         {
             var buffer = array.AsMemory(0, batchSize);
             var writtenCount = await outboxRepository.LockAndWrite(buffer, lockRenewalTimer.InstanceId, batchSize, _outboxSettings.MaintainSequence, lockRenewalTimer.LockDuration, cts.Token);

             var outboxMessages = buffer.Slice(0, writtenCount);

             var (RunAgain, Count) = await ProcessMessages(outboxRepository, outboxMessages, compositeMessageBus, messageBusTarget, cts.Token);
         }
         finally
         {
             messagePooler.Return(array);  // <= 2
         }
     } while ();
 }

ps. There's an internal mechanism here and I think we can play with it.

After the release of C# 8, all of its features were available only in projects compatible with .NET Standard version 2.1 or higher.

https://stackoverflow.com/questions/406485/array-slices-in-c-sharp/65898435#65898435

public interface IOutboxRepository
{
    Task<int> LockAndWrite(OutboxMessage[] buffer, string instanceId, int batchSize, ... CancellationToken token);

3. How many databases don't support Guid?

-- I think not that many.

Type conversion and working with Reflections looks a bit heavy. I'm more concerned about GC performance here. I would return the Id field to the OutboxMessage class...

3. How many databases don't support Guid?

-- I think not that many.

Type conversion and working with Reflections looks a bit heavy. I'm more concerned about GC performance here. I would return the Id field to the OutboxMessage class...

If we can stick with the Guid type, it is much simpler, and yes then you don't have to create wrapper around OutboxMessage and expose Guid Id property as it was.
Where do you see the Reflections in there?

2. Performance IOutboxRepository (there's some testing to be done), LockAndWrite instead of LockAndSelect for ArrayPool
   ...

Yes, these are nice ideas to incorporate. As always to be compatible with netstandard2.0 some #if preprocessor will have to be done (working without the benefits of these new memory types prior net8.0). Remember SMB multi-targets netstandard2.0, net6.0 and net8.0. I don't want to go to netstandard2.1 just yet to have a broader reach.

1. I'd add new interface ITimeResolver

https://andrewlock.net/exploring-the-dotnet-8-preview-avoiding-flaky-tests-with-timeprovider-and-itimer/?ref=grantwinney.com

// +
public interface ITimeResolver
{
    DateTime GetUtcNow();
}

Yes, this could be added, I suggest to the SlimMessageBus.Host layer so that all transports can benefit.

What are the next steps here @dundich?
Would you like anything particular from me (e.g. evolve my draft PR)?
Do you want to start evolving your PR along the lines of #314 with your suggestions above?

Let me know.

Where do you see the Reflections in there?

• Reflections in my brain - sorry )

Would you like anything particular from me (e.g. evolve my draft PR)??

• You seem to have far more knowledge on this issue than I do. It's up to you.

Do you want to start evolving your PR along the lines of #314 with your suggestions above?

• I'm going to start Outbox.Pg using the master branch

ps

4. [Host.Outbox] optimistic mode - hybrid strategy? #313

https://masstransit.io/documentation/patterns/newid

I can help with some of the initial work and perhaps evolve my PR to enable some preparations for your Postgres adaptation of Outbox. I think it could simply be a dialect setting on the existing Outbox.Sql package (no need to create an entirely new package solely for Postgres).

The NewId is the introduction of sequential Guids/UUIDs per what you wrote earlier and need. We could have something similar added to the SlimMessageBus.Host, so that other plugins and providers can benefit from that prior NET9 - especially the Outbox.

@dundich You can see where I am going with my latest thinking in #315.
Down the road SMB will also start to target net9 preview to take advantage of the new Guid UUIDv7 methods.