A new feature in the big Marten 7.0 release this weekend is an alternative to add numeric revisions to a document as a way of enforcing optimistic concurrency checks.
First off, from Martin Fowler’s seminal Patterns of Enterprise Application Architecture (which is just visible to me on my book case across the room as I write this even though it’s 20 years old now), an Optimistic Offline Lock is:
Prevents conflicts between concurrent business transactions by detecting a conflict and rolling back the transaction.
David Rice
In a simple usage, let’s say we’re building some kind of system to make reservations for restaurants. Logically, we’d have a document named Reservation, and we’ve decided that we want to use the numeric revisioning on this document. That document type could look something like this:
// By implementing the IRevisioned
// interface, we're telling Marten to
// use numeric revisioning with this
// document type and keep the version number
// on the Version property
public class Reservation: IRevisioned
{
public Guid Id { get; set; }
// other properties
public int Version { get; set; }
}
Now, let’s see this in action just a little bit:
public static async Task try_revisioning(IDocumentSession session, Reservation reservation)
{
// This will create a new document with Version = 1
session.Insert(reservation);
// "Store" is an upsert, but if the revisioned document
// is all new, the Version = 1 after changes are committed
session.Store(reservation);
// If Store() is called on an existing document
// this will just assign the next revision
session.Store(reservation);
// *This* operation will enforce the optimistic concurrency
// The supplied revision number should be the *new* revision number,
// but will be rejected with a ConcurrencyException when SaveChanges() is
// called if the version
// in the database is equal or greater than the supplied revision
session.UpdateRevision(reservation, 3);
// This operation will update the document if the supplied revision
// number is greater than the known database version when
// SaveChanges() is called, but will do nothing if the known database
// version is equal to or greater than the supplied revision
session.TryUpdateRevision(reservation, 3);
// Any checks happen only here
await session.SaveChangesAsync();
}
Summary
In the end, this is another alternative to the older Guid based version tracking that Marten has supported since 1.0. I don’t know about you, but I can certainly read and understand an integer much more easily than a random string of letters, numbers, and dashes.
In reality though, this feature was specifically built as a prerequisite to some serious improvements to the asynchronous projection support in Marten. Time and ambition permitting, the next Marten 7.0 blog post will show how Marten can support the strongly consistent “write model” projections you need for command processing while also being performant and allowing for zero downtime projection rebuilds.
Marten 7.0 is released to the wild as of right now! Before getting into the highlights of what’s improved in this release, let’s go right to thanking some of the folks who made big contributions to this release either through code, testing, or feedback:
Vedran Zakanj for sponsoring Marten and also contributing ideas around schema management
And a huge thanks to Lucas Wyland for specifically sponsoring the improved LINQ provider work with an equally huge apology from me on how long that took to finish
And to many more community members who helped improve Marten throughout this very long release cycle.
Highlights
This was a huge release, if not nearly as disruptive as Marten 4 was several years ago. I do not anticipate a lot of issues for users upgrading from Marten 6 to Marten 7, but see the migration guide for more details.
The highlights of Marten 7 are:
The LINQ query support was given a large overhaul that both expanded its supported use cases and led to significantly improved performance of many common sub collection queries — which has been a large complaint and request for improvement from the Marten community for several years
A “Partial” document update capability using native PostgreSQL functionality with no JavaScript in sight! That’s been a long requested capability.
The very basic database execution pipeline underneath Marten was largely rewritten to be far more parsimonious with how it uses database connections and to take advantage of more efficient Npgsql usage. We think these changes will make Marten both more efficient overall (these changes reduced the number of object allocations by quite a bit) and help system health through using fewer database connections
We introduced Polly for resiliency to transient errors like network hiccups or a temporarily overloaded database and actually made Marten able to properly execute retries of database writes and database reads
The “async daemon” subsystem was somewhat rewritten with substantial improvements for application scalability. The asynchronous projection support also has an all new scheme for resiliency that we think will be a big improvement for our users
An option to utilize Marten’s recommended FetchForWriting() API for “write model” aggregation with asynchronous projections. This may sound like a lot of mumbo jumbo, but it’s vital because this enables the next bullet point
The ability to do zero downtime deployments of some projection changes as well as to do blue/green deployments of revisioned projections. Much more on this later this week.
A new alternative for “revisioned” documents with a numeric version as an alternative to Marten’s existing GUID based versioning scheme for optimistic concurrency
We’ll see how big of a deal this turns out to be, but Marten 7 enables the usage of Project Aspire with Marten
As time permits, I will be writing deep dive blog posts on each of the individual bullet points above over the next couple weeks — partially as a way to force the completion of some not perfectly updated documentation!
You can Place a Technical Bet on Marten
There’s frequently an understandable hesitation on the part of software shops to take a bet on an open source tool as a critical piece of their technical infrastructure — and that’s sometimes worse in the .NET ecosystem where OSS adoption isn’t as widespread. All that aside, I’m here to tell you that you can feel safe making a large technical bet on Marten because:
Marten is already a very mature project that has been in production usage since its 1.0 release in 2016
While Marten doesn’t have every single issue around production support, deployments, and schema management fixed yet, we’ve got a detailed roadmap to shore up any remaining weaknesses of the tool and we’re in this for the long haul!
PostgreSQL itself is a very successful open source project that continuously innovates and provides a very solid technical foundation for Marten itself
We’ve invested a lot of time into refining Marten’s usability over the years and we think that attention to detail shines through
JasperFx Software offers support contracts and consulting work for Marten users
In conjunction with Wolverine’s integration with Marten, the full “Critter Stack” provides a very efficient and usable stack for Event Driven Architecture using Event Sourcing and a CQRS architecture
While Marten 7.0 made some significant improvements for scalability, the forthcoming “Critter Stack Pro” commercial add on tooling will take Marten to much larger data sets and transactional throughput
Because Marten does target .NET, it’s worth pointing out that at this point, Microsoft has no technical offerings for Event Sourcing and that will absolutely contribute to Marten’s viability
What’s Next and Summary
A lot of big, important, long requested, long planned features and improvements did not make the cut for V7. I blogged last week about the current roadmap for the entire Critter Stack. Moreover, some open bugs didn’t make it into 7.0 as well. And let’s be honest, there’s going to be a slew of bug reports streaming in this week when folks try out new 7.0 features and encounter usage permutations we didn’t anticipate. I’ve finally learned my lesson and made this release after having gotten some rest to be ready for whatever the issues turn out to be in the morning.
Wolverine 2.0 will also follow shortly, but the roadmap for that is pretty well just upgrading to Marten 7, dumping .NET 6, and fixing some low hanging fruit issues and requests before a release in the next couple days.
We’ll jump on whatever those Marten 7 issues turn out to be and all the questions about “what about *my* use case I don’t see on your list!” starting tomorrow, but for right now, this was a huge release filled with all kinds of substantial improvements that for the first time included significant client sponsored requests and please don’t steal my sunshine!
Isaac Levin was kind enough to have me on his Coffee & Open Source show to talk about a variety of topics around technology and my involvement with OSS work.
I need to update my profile here and there, that picture was taken on my late grandparents farm around Christmas of 2010 outside the titular Jasper, MO
I’d say that my time in OSS has long been valuable in terms of increased technical skillset and occasionally through opportunities that arose because of my OSS tools. It’s just now though that I’m finally living out my longstanding dream to make my “Critter Stack” OSS work (Marten & Wolverine) be my actual job as part of JasperFx Software.
Just to call a few highlights and to add to our conversation after having some time to think about things:
I made a double edged bit of advice at the end to “take your shot” when you have a technical idea that could become your job, but followed by an exhortation to stop working on something that isn’t bringing you joy or opportunities.
Unfortunately, failure is an awesomely effective teacher — if you let it be. I feel like the Critter Stack tools are succeeding right now, and plenty of that is due to some harsh lessons learned from my earlier failures in OSS.
OSS projects can succeed with a mix of having a conceptual idea or approach that appeals to enough folks, a dedicated core team of contributors like Oskar and Babu, and an enthusiastic and patient community that helps with suggestions, bug reports, and contributions. I called out Wolverine especially as a tool whose usability has largely been driven by the feedback of several early adopters. Moreover, one of the hard lessons learned from my earlier failure with FubuMVC is how important it is to get enough user feedback to sand off rough edges with a tool’s usability or documentation.
I personally find it very gratifying to be working on my projects, carrying out my vision, and generally having my hand on the steering wheel of Marten and Wolverine. I’m also enjoying the hands on consulting engagements I’m doing with the current JasperFx clients and making a positive difference for them. The obvious takeaway for me — and probably for a great number of you out there as well — is that I am much happier when I feel like I have significant ownership over the work and that my contributions are respected and valued by the customer, management, product owner, or colleagues. I’ve been consistently miserable in jobs or roles where I didn’t have either of those two things.
From some notes that Oskar, Babu, and I banged out this past week, so keep your expectations for the quality of prose here! Notes in bold are my updates since this original document was banged out last weekend.
Marten 7.0
Try to release Marten 7.0 no later than early next week. This is admittedly based on JasperFx client deliverables.
Blue/green & zero downtime deployment. Ongoing work that just needs more testing at this point. This includes the projection version stuff. Actually all working locally, but my development branch is rebased on the daemon stuff, so I’d like that to go in first. Done.
Projection Snapshots – I’d really like to see this mostly land in Critter Stack Pro. Probably not happening until 2nd quarter 2024
First class subscriptions from the event store to Wolverine transports – might be in Wolverine 2.0 proper. Dunno. Not sure yet
Async projection optimizations – Probably not happening until 2nd quarter 2024
2nd level caching for aggregates
Rebuild single stream projections stream by stream
Allow for selective identity map usage of reference types.
Batched data lookups – so you can keep projections from doing chatty data access
Allow grouping logic to express optimization hints like “no data access required” or “requires aggregate state”. That could be used to optimize projection rebuilds
Wolverine 2.0
Discovery and activation of new tenant databases at runtime (client deliverable). Done.
Update to Marten 7
Project Aspire? Wolverine 2.1? This is a little more involved, so I’m not sure yet when this lands. Probably in Wolverine 2.1.
Marten 7.1
Open Telemetry Support – Sean Farrow is working on this. I don’t think it’s going to be a breaking change, so could float to 7.1. Very Basic
Sharding the event store tables – I’d love to do this sooner, and would love to stretch this in. I’m saying that we would tackle the is archived / not archived sharding in a first pass, then come back w/ fancier sharding possibilities later. This would have a potentially huge positive implication for Marten event store scalability.
The ability to “emit” new events in the async daemon during the course of processing asynchronous projections. I think this is going to take some spikes and analysis, so we gotta commit to this ASAP if it’s going into 7.0. This is falling to Marten 7.1
First class subscriptions. Hot, cold, replay, whatever. I just want a little more time and space. Does this require any breaking changes in the daemon we might want to deal with right now though? Very likely dropping to Marten 7.1
Custom event type naming strategy – it’s a breaking change to the API I think. I don’t think it’s huge though – little pluggable strategy. Can be additive.
Optimize inline projections in FetchForWriting()? Idea here is to force aggregates that are calculated Inline (or Async maybe) that are queried in FetchForWriting() be forced to use the identity map for just that document type. That does a lot to optimize the typical “aggregate handler workflow” by avoiding the current double fetching of the document when you are using lightweight sessions. Strong candidate to drop down to 7.1
Marten 7.Later
Downcasters – I vote to put this into Critter Stack Pro all the way
Marten 8.0???
More advanced Event Store partitioning
Wolverine 2.1
Likely a focus on the Wolverine.HTTP backlog
Options for strict ordering requirements of event or message processing
Hey, did you know that JasperFx Software is ready for formal support plans for Marten and Wolverine? Not only are we making the “Critter Stack” tools be viable long term options for your shop, we’re also interested in hearing your opinions about the tools and how they should change.We’re also certainly open to help you succeed with your software development projects on a consulting basis whether you’re using any part of the Critter Stack or some completely different .NET server side tooling.
In the continuing saga of trying to build a sustainable business model around Marten and Wolverine (the “Critter Stack”), JasperFx Software is quietly building a new set of tools code named “Critter Stack Pro” as a commercially licensed add on to the MIT-licensed OSS core tools.
While there’s some very serious progress on a potential management user interface tool for Marten & Wolverine features underway, the very first usable piece will be a new library for scaling Marten’s asynchronous projection model by much more efficiently distributing work across a clustered application than Marten by itself can today.
In the first wave of work, we’re aiming for this feature set:
When using a single Marten database, the execution of asynchronous projections will be distributed evenly across the application cluster
When using multiple Marten databases for multi-tenancy, the execution of asynchronous projections will be distributed by database and evenly across the application cluster
In blue/green deployments, “Critter Stack Pro” will be able to ensure that all known versions of each projection and database are executing in a suitable “blue” or “green” node within the application cluster
When using multiple Marten databases for multi-tenancy and also using the new dynamic tenant capability in Marten 7.0, “Critter Stack Pro” will discover the new tenant databases at runtime and redistribute projection work across the application cluster
“First class subscriptions” of Marten events with strict ordering through any of Wolverine’s supported messaging transports (locally, Rabbit MQ, Kafka, Azure Service Bus, AWS SQS, soon to be more!).
We’re certainly open to more suggestions from long term and potential users about what other features would make “Critter Stack Pro” a must have tool for your production environment. Trigger projection projection rebuilds on demand? Apply a new subscription? Pause a subscription? Force “Critter Stack Pro” to redistribute projections across the cluster? Smarter distribution algorithms based on predicted load? Adaptive distribution based on throughput?
And do know that we’re already working up a potential user interface for visualizing and monitoring Marten and Wolverine’s behavior at runtime.
This new product (knock on wood) is going to be delivered to a JasperFx customer within the next week or two for integration into their systems using Marten 7.0 and Wolverine 2.0 (also not coincidentally forthcoming at the end of the next week). I’m not going to commit to when this will be generally available, but I’d sure hope it’s sometime in the 2nd quarter this year.
Hey, did you know that JasperFx Software is ready for formal support plans for Marten and Wolverine? Not only are we making the “Critter Stack” tools be viable long term options for your shop, we’re also interested in hearing your opinions about the tools and how they should change.We’re also certainly open to help you succeed with your software development projects on a consulting basis whether you’re using any part of the Critter Stack or some completely different .NET server side tooling.
Marten 7.0.0 RC just dropped on Nuget with some new fixes and some very long awaited enhancements that I’m personally very excited about. The docs need to catch up, but the 7.0 release is shaping up for next week (come hell or high water). One of the new highlights for Marten 7 that was sponsored by a JasperFx Software client was the ability to add new tenant databases at runtime when using Marten’s “database per tenant” strategy.
It’s not documented yet (I’m working on it! I swear!), but here’s a sneak peek from an integration test:
// Setting up a Host with Multi-tenancy
_host = await Host.CreateDefaultBuilder()
.ConfigureServices(services =>
{
services.AddMarten(opts =>
{
// This is a new strategy for configuring tenant databases with Marten
// In this usage, Marten is tracking the tenant databases in a single table in the "master"
// database by tenant
opts.MultiTenantedDatabasesWithMasterDatabaseTable(ConnectionSource.ConnectionString, "tenants");
opts.RegisterDocumentType<User>();
opts.RegisterDocumentType<Target>();
opts.Projections.Add<TripProjectionWithCustomName>(ProjectionLifecycle.Async);
})
.AddAsyncDaemon(DaemonMode.Solo)
// All detected changes will be applied to all
// the configured tenant databases on startup
.ApplyAllDatabaseChangesOnStartup();
}).StartAsync();
With this model, Marten is setting up a table named mt_tenant_databases to store with just two columns:
tenant_id
connection_string
At runtime, when you ask for a new session for a specific tenant like so:
using var session = store.LightweightSession("tenant1");
This new Marten tenancy strategy will first look for a database with the “tenant1” identifier its own memory, and if it’s not found, will try to reach into the database table to “find” the connection string for this newly discovered tenant. If a record is found, the new tenancy strategy caches the information, and proceeds just like normal.
Now, let me try to anticipate a couple questions you might have here:
Can Marten track and apply database schema changes to new tenant databases at runtime? Yes, Marten does the schema check tracking on a database by database basis. This means that if you add a new tenant database to that underlying table, Marten will absolutely be able to make schema changes as needed to just that tenant database regardless of the state of other tenant databases.
Will the Marten command line tools recognize new tenant databases? Yes, same thing. If you call dotnet run -- marten-apply for example, Marten will do the schema migrations independently for each tenant database, so any outstanding changes will be performed on each tenant database.
Can Marten spin up asynchronous projections for a new tenant database without requiring downtime? Yes! Check out this big ol’ integration test proving that the new Marten V7 version of the async daemon can handle that just fine:
[Fact]
public async Task add_tenant_database_and_verify_the_daemon_projections_are_running()
{
// In this code block, I'm adding new tenant databases to the system that I
// would expect Marten to discover and start up an asynchronous projection
// daemon for all three newly discovered databases
var tenancy = (MasterTableTenancy)theStore.Options.Tenancy;
await tenancy.AddDatabaseRecordAsync("tenant1", tenant1ConnectionString);
await tenancy.AddDatabaseRecordAsync("tenant2", tenant2ConnectionString);
await tenancy.AddDatabaseRecordAsync("tenant3", tenant3ConnectionString);
// This is a new service in Marten specifically to help you interrogate or
// manipulate the state of running asynchronous projections within the current process
var coordinator = _host.Services.GetRequiredService<IProjectionCoordinator>();
var daemon1 = await coordinator.DaemonForDatabase("tenant1");
var daemon2 = await coordinator.DaemonForDatabase("tenant2");
var daemon3 = await coordinator.DaemonForDatabase("tenant3");
// Just proving that the configured projections for the 3 new databases
// are indeed spun up and running after Marten's new daemon coordinator
// "finds" the new databases
await daemon1.WaitForShardToBeRunning("TripCustomName:All", 30.Seconds());
await daemon2.WaitForShardToBeRunning("TripCustomName:All", 30.Seconds());
await daemon3.WaitForShardToBeRunning("TripCustomName:All", 30.Seconds());
}
At runtime, if the Marten V7 version of the async daemon (our sub system for building asynchronous projections constantly in a background IHostedService) is constantly doing “health checks” to make sure that *some process* is running all known asynchronous projections on all known client databases. Long story, short, Marten 7 is able to detect new tenant databases and spin up the asynchronous projection handling for these new tenants with zero downtime.
There’s a helluva lot more new stuff and big improvements to the old stuff in Marten coming in V7, but this one was a definite highlight.
Look for the official Marten 7.0 release next week!
Nick Chapsas just released a video about Wolverine with his introduction and take on the framework. Not to take anything away from the video that was mostly positive, but I thought there were quite a few misconceptions about Wolverine evident in the comments and some complaints I would like to address so I can stop fussing about this and work on much more important things.
First off, what is Wolverine? Wolverine is a full blown application framework and definitely not merely a “library,” so maybe consider that when you are judging the merits of its opinions or not. More specifically, Wolverine is a framework built around the idea of message processing where “messages” could be coming from inline invocation like MediatR or local in process queues or external message brokers through asynchronous messaging ala the much older MassTransit or NServiceBus frameworks. In addition, Wolverine’s basic runtime pipeline has also been adapted into an alternative HTTP endpoint framework that could be used in place of or as a complement to MVC Core or Minimal API.
I should also point out that Wolverine was largely rescued off the scrap heap and completely rebooted specifically to work in conjunction with Marten as a full blow event driven architecture stack. This is what we mean when we say “Critter Stack.”
In its usage, Wolverine varies quite a bit from the older messaging and mediator tools out there like NServiceBus, MassTransit, MediatR, Rebus, or Brighter.
Basically all of these existing tools one way or another force you to constrain your code within some kind of “IHandler of T” abstraction something like this:
By and large, these frameworks assume that you will be using an IoC container to fill any dependencies of the actual message handler classes through constructor injection. Part of the video I linked to was the idea that Wolverine was very opinionated, so let’s just get to that and see how Wolverine very much differs from all the older “IHandler of T” frameworks out there.
Wolverine’s guiding philosophies are to:
Reduce code ceremony and minimize coupling between application code and the surrounding framework. As much as possible — and it’s an imperfect world so the word is “minimize” and not “eliminate” — Wolverine attempts to minimize the amount of code cruft from required inheritance, marker interfaces, and attribute usage within your application code. Wolverine’s value proposition is that lower ceremony code leads to easier to read code that offsets any disadvantages that might arise from using conventional approaches
Promote testability — both by helping developers structure code in such a way that they can keep infrastructure concerns out of business logic for easy unit testing and to facilitate effective automated integration testing as well. I’ll throw this stake in the ground right now, Wolverine does much more to promote testability than any other comparable framework that I’m aware of, and I don’t mean just .NET frameworks either (Proverbs 16:18 might be relevant here, but shhh).
“It should just work” — meaning that as much as possible, Wolverine should try to set up infrastructural state (database schemas, message broker configuration, etc.) that your application depends on for an efficient developer experience
Bake in logging, auditing, and observability so that developers don’t have to think about it. This is partially driven by the desire for low code ceremony because nothing is more repetitive in systems than copy/paste log statements every which way
Be as performant as possible. Wolverine is descended and influenced by an earlier failed OSS project called FubuMVC that strived for very low code ceremony and testability, but flunked on performance and how it handled “magic” conventions. Let’s just say that failure is a harsh but effective teacher. In particular, Wolverine tries really damn hard to reduce the number of object allocations and dictionary lookups at runtime as those are usually the main culprits of poor performance in application frameworks. I fully believe that before everything is said and done, that Wolverine will be able to beat the other tools in this space because of its unique runtime architecture.
A Wolverine message handler might look something like this from one of our samples in the docs that happens to use EF Core for persistence:
public static class CreateItemCommandHandler
{
public static ItemCreated Handle(
// This would be the message
CreateItemCommand command,
// Any other arguments are assumed
// to be service dependencies
ItemsDbContext db)
{
// Create a new Item entity
var item = new Item
{
Name = command.Name
};
// Add the item to the current
// DbContext unit of work
db.Items.Add(item);
// This event being returned
// by the handler will be automatically sent
// out as a "cascading" message
return new ItemCreated
{
Id = item.Id
};
}
}
There’s a couple things I’d ask you to notice right off the bat that will probably help inform you if you’d like Wolverine’s approach or not:
There’s no required IHandler<T> type interface. Nor do we require any kind of IMessage/IEvent/ICommand interface on the message type itself
The method signatures of Wolverine message handlers are pretty flexible. Wolverine can do “method injection” like .NET developers are used to now in Minimal API or the very latest MVC Core where services from the IoC container are pushed into the handler methods via method parameters (Wolverine will happily do constructor injection just like you would in other frameworks as well). Moreover, Wolverine can even do different things with the handler responses like “know” that it’s a separate message to publish via Wolverine or a “side effect” that should be executed inline. Heck, the message handlers can even be static classes or methods to micro-optimize your code to be as low allocation as possible.
Wolverine is not doing any kind of runtime Reflection against these handler methods, because as a commenter pointed out, this would indeed be very slow. Instead, Wolverine is generating and compiling C# code at runtime that wraps around your method. Going farther, Wolverine will use your application’s DI configuration code and try to generate code that completely takes the place of your DI container at runtime. Some folks complain that Wolverine forces you to use Lamar as the DI container for your application, but doing so enabled Wolverine to do the codegen the way that it is. Nick pushed back on that by asking what if the built in DI container becomes much faster than Lamar (it’s the other way around btw)? I responded by pointing out that the fasted DI container is “no DI container” like Wolverine is able to do at runtime.
The message handlers are found by default through naming conventions. But if you hate that, no worries, there are options to use much more explicit approaches. Out of the box, Wolverine also supports discovery using marker interfaces or attributes. I don’t personally like that because I think it “junks up the code”, but if you do, you can have it your way.
The handler code above was written with the assumption that it’s using automatic transactional middleware around it all that handles the asynchronous code invocation, but if you prefer explicit code, Wolverine happily lets you eschew any of the conventional magic and write explicit code where you would be completely in charge of all the EF Core usage. The importance of being able to immediately bypass any conventions and drop into explicit code as needed was an important takeaway from my earlier FubuMVC failure.
Various Objections to Wolverine
It’s opinionated, and I don’t agree with all of Wolverine’s opinions. This one is perfectly valid. If you don’t agree with the idiomatic approach of a software development tool, you’re far better off to just pick something else instead of fighting with the tool and trying to use it differently than its idiomatic usage. That goes for every tool, not just Wolverine. If you’d be unhappy using Wolverine and likely to gripe about it online, I’d much rather you go use MassTransit.
Runtime reflection usage? As I said earlier, Wolverine does not use reflection at runtime to interact with the message handlers or HTTP endpoint methods
Lamar is required as your IoC tool. I get the objection to that, and other people have griped about that from time to time. I’d say that the integration with Lamar enables some of the very important “special sauce” that makes Wolverine different. I will also say that at some point in the future we’ll investigate being able to at least utilize Wolverine with the built in .NET DI container instead
Oakton is a hard dependency, and why is Wolverine mandating console usage? Yeah, I get that objection, but I think that’s very unlikely to ever really matter much. You don’t have to use Oakton even though it’s there, but Wolverine (and Marten) both heavily utilize Oakton for command line diagnostics that can do a lot for infrastructure management, environment checks, code generation, database migrations, and important diagnostics that help users unravel and understand Wolverine’s “magic”. We could have made that all be separate adapter package or add ons, but from painful experience, I know that the complexity of usage and development of something like Wolverine goes up quite a bit with the number of satellite packages you use and require — and that’s already an issue even so with Wolverine. I did foresee the Lamar & Oakton objections, but consciously decided that Wolverine development and adoption would be easier — especially early on — by just bundling things together. I’d be willing to reconsider this in later versions, but it’s just not up there in ye olde priority list
There are “TODO” comments scattered in the documentation website! There’s a lot of documentation up right now, and also quite a few samples. That work is never, ever done and we’ll be improving those docs as we go. The one thing I can tell you definitively about technical documentation websites is that it’s never good enough for everyone.
Hey, did you know that JasperFx Software is ready for formal support plans for Marten and Wolverine? Not only are we making the “Critter Stack” tools be viable long term options for your shop, we’re also interested in hearing your opinions about the tools and how they should change.We’re also certainly open to help you succeed with your software development projects on a consulting basis whether you’re using any part of the Critter Stack or some completely different .NET server side tooling.
I checked this morning, and Marten’s original 1.0 release was in September of 2016. Since then we as a community have been able to knock down several big obstacles to user adoption, but one pernicious concern of new users was the ability to scale the asynchronous projection support to very large loads as Marten today only supports a “hot/cold” model where all projections run in the same active process.
Two developments are going to finally change that in the next couple weeks. First off, the next Marten 7 beta is going to have a huge chunk of work on Marten’s “async daemon” process that potentially distributes work across multiple nodes at runtime.
By (implied) request:
We very much would like to know more about this new 🔥 hotness…
"If targeting a single database, Marten possibly runs projections on separate nodes"
If you are targeting a single database, Marten will do its potential ownership of each projection independently. We’re doing this by using PostgreSQL advisory locks for the determination of ownership on a projection by projection basis. At runtime, we’re using a little bit of randomness so that if you happen to start up multiple running application nodes at the same time, the different nodes will start checking for that ownership at random times and do so with a random order of the various projections. It’s not fool proof by any means, but this will allow Marten to potentially spread out the projections to different running application instances.
If you are using multi-tenancy through separate databases, Marten’s async daemon will similarly do an ownership check by database, and keep all the projections for a single database running on the same node. This is done with the theory that this should potentially reduce the number of database connections used overall by your system. As in the previous bullet for a single tenant, there’s some randomness introduced so each application instance doesn’t try to get ownership of the same databases at the same time and potentially cause dead lock situations. Likewise, Marten is randomizing the order in which it attempts to check the ownership of different databases so there’s a chance this strategy will distribute work across multiple nodes.
There’s some other improvements so far (with hopefully much more to follow) that we hope will increase the throughput of asynchronous projections, especially for projection rebuilds.
I should also mention that a JasperFx Software client has engaged us to improve Marten & Wolverine‘s support for dynamic utilization of per tenant databases where both Marten & Wolverine are able to discover new tenant databases at runtime and activate all necessary support agents for the new databases. That dynamic tenant work in part led to the async projection work I described above.
Let’s go even farther…
I’ll personally be very heads down this week on some very long planned work (sponsored by a JasperFx Software client!!!) for a “Critter Stack Pro” tool set to extend Marten’s event store to much larger data sets and throughput. This will be the first of a suite of commercial add on tools to the “Critter Stack”, with the initial emphasis being:
The ability to more effectively distribute asynchronous projection work across the running instances of the application using a software-based “agent distribution” already built into Wolverine. We’ll have some simple rules for how projections are distributed upfront, but I’m hoping to evolve into adaptive rules later that can adjust the distribution based on measured load and performance metrics
Zero-downtime deployments of Marten projection changes
Blue/green deployments of revisioned Marten projections and projected aggregates, meaning that you will be able to deploy a new version of a Marten projection in some running instances of a server applications while the older version is still functional in other running instances
I won’t do anything silly like put a timeframe around this, but the “Critter Stack Pro” will also include a user interface management console to watch and control the projection functionality.
A very important part of any event sourcing architecture is actually being able to interpret the raw events representing the current (or past) state of the system. That’s where Marten’s “Projection” subsystem comes into play as a way to compound a stream of events into a stateful object representing the whole state.
Most of the examples you’ll find of Marten projections will show you one of the aggregation recipes that heavily lean on conventional method signatures with Marten doing some “magic” around those method names, like this simple “self-aggregating” document type:
public record TodoCreated(Guid TodoId, string Description);
public record TodoUpdated(Guid TodoId, string Description);
public class Todo
{
public Guid Id { get; set; }
public string Description { get; set; } = null!;
public static Todo Create(TodoCreated @event) => new()
{
Id = @event.TodoId,
Description = @event.Description,
};
public void Apply(TodoUpdated @event)
{
Description = @event.Description;
}
}
Notice the Apply() and Create() methods in the Todo class above. Those are following a naming convention that Marten uses to “know” how to update a Todo document with new information from events.
I (and by “I” I’m clearly taking responsibility for any problems with this approach) went down this path with Marten V4 as a way to make some performance optimizations at runtime. This approach goes okay if you stay well within the well lit path (create, update, maybe delete the aggregate document), but can break down when folks get “fancy” with things like soft deletes. Or all too frequently, this approach can confuse users when the problem domain gets more complex.
There’s an escape hatch though. We can toss aside all the conventional magic and the corresponding runtime magic that Marten does for these projections and just write some explicit code.
Using Marten’s “CustomProjection” recipe — which is just a way to use explicit code to do aggregations of event data — we can write the same functionality as above with this equivalent:
public record TodoCreated(Guid TodoId, string Description);
public record TodoUpdated(Guid TodoId, string Description);
public class Todo
{
public Guid Id { get; set; }
public string Description { get; set; } = null!;
}
// Need to inherit from CustomProjection
public class TodoProjection: CustomProjection<Todo, Guid>
{
public TodoProjection()
{
// This is kinda meh to me, but this tells
// Marten how to do the grouping of events to
// aggregated Todo documents by the stream id
Slicer = new ByStreamId<Todo>();
// The code below is only valuable as an optimization
// if this projection is running in Marten's async
// daemon to help the daemon filter candidate events faster
IncludeType<TodoCreated>();
IncludeType<TodoUpdated>();
}
public override ValueTask ApplyChangesAsync(DocumentSessionBase session, EventSlice<Todo, Guid> slice, CancellationToken cancellation,
ProjectionLifecycle lifecycle = ProjectionLifecycle.Inline)
{
var aggregate = slice.Aggregate;
foreach (var e in slice.AllData())
{
switch (e)
{
case TodoCreated created:
aggregate ??= new Todo { Id = slice.Id, Description = created.Description };
break;
case TodoUpdated updated:
aggregate ??= new Todo { Id = slice.Id };
aggregate.Description = updated.Description;
break;
}
}
// This is an "upsert", so no silly EF Core "is this new or an existing document?"
// if/then logic here
session.Store(aggregate);
return new ValueTask();
}
}
Putting aside the admitted clumsiness of the “slicing” junk, our projection code is just a switch statement. In hindsight, the newer C# switch expression syntax was just barely coming out when I designed the conventional approach. If I had it to do again, I think I would have focused harder on promoting the explicit logic and bypassed the whole conventions + runtime code generation thing for aggregations. Oh well.
For right now though, just know that you’ve got an escape hatch with Marten projections to “just write some code” any time the conventional approach causes you the slightest bit of grief.
Hey, did you know that JasperFx Software is ready for formal support plans for Marten and Wolverine? Not only are we trying to make the “Critter Stack” tools be viable long term options for your shop, we’re also interested in hearing your opinions about the tools and how they should change.We’re also certainly open to help you succeed with your software development projects on a consulting basis whether you’re using any part of the Critter Stack or any other .NET server side tooling.
A lot of pull requests and bug fixes just happened to land today for both Marten and Wolverine. In order, we’ve got:
Marten 7.0.0 Beta 5
Marten 7.0.0 Beta 5 is actually quite a big release and a major step forward on the road to the final V7 release. Besides some bug fixes, I think the big highlights are:
Marten finally gets the long awaited “Partial Update” model that only depends on native PosgreSQL features! Huge addition from Babu. If you’re coming to Marten from MongoDb, or only would if Marten had the ability to modify documents without first having to load the whole thing, well now you can! No PLv8 extension necessary!
We pushed through a new low level execution model that’s more parsimonious about how long database connections are kept open that should help applications using Marten scale to more concurrent transactions. This should also help folks using Marten in conjunction with Hot Chocolate as now IQuerySession could be used in multiple threads in parallel.
Marten now uses Polly internally for retries on transient errors, and the “retry” functionality actually works now (it didn’t actually do anything useful before, as I shamefully refuse to make eye contact with you).
Several fixes around full text indexes that were blocking some folks
Wolverine 1.16.0
Wolverine 1.16.0 came out today with a couple additions and fixes related to MQTT or Rabbit MQ message publishing to topics. As an example, here’s some new functionality with Rabbit MQ message publishing:
You can specify publishing rules for messages by supplying the logic to determine the topic name from the message itself. Let’s say that we have an interface that several of our message types implement like so:
public interface ITenantMessage
{
string TenantId { get; }
}
Let’s say that any message that implements that interface, we want published to the topic for that messages TenantId. We can implement that rule like so:
using var host = await Host.CreateDefaultBuilder()
.UseWolverine((context, opts) =>
{
opts.UseRabbitMq();
// Publish any message that implements ITenantMessage to
// a Rabbit MQ "Topic" exchange named "tenant.messages"
opts.PublishMessagesToRabbitMqExchange<ITenantMessage>("tenant.messages",m => $"{m.GetType().Name.ToLower()}/{m.TenantId}")
// Specify or configure sending through Wolverine for all
// messages through this Exchange
.BufferedInMemory();
})
.StartAsync();
Wolverine 2.0 Alpha 1
Knock on wood, if the GitHub Action & Nuget gods all agree, there will be a Wolverine 2.0 alpha 1 set of Nugets available that’s just Wolverine 1.16, but targeting the very latest Marten 7 betas as somebody asks me just about every single day when that’s going to be ready.
Enjoy! And don’t tell me about any problems with these releases until Monday!
Summary
I had a very off week as I struggled with a cold, a busy personal life, and way more Zoom meetings than I normally have. All the same, getting to spit out these three releases today makes me feel like Bill Murray here: