marten | NET Transactional Document DB and Event Store on PostgreSQL | Microservice library
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kandi X-RAY | marten Summary
.NET Transactional Document DB and Event Store on PostgreSQL
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QUESTION
I have web app with two databases:
- EventStoreDB - for events
- PostgreSQL + Marten - for projections
For subscription and add data from eventstore to postgres I use this sample sample But, when I make create operation and got success result, next I am trying load new object from postgres, postgres has not my new object.
How can I make "events applying from eventstore to postgres faster or sync" ?
...ANSWER
Answered 2022-Jan-29 at 20:19Event-sourced systems by definition have a time lag between an event being stored in an event store, and it is projected to a read model. The lag is always there unless you apply the event synchronously to an in-memory read model when you commit the event to the store. But that approach would limit you to run your service as a single instance, otherwise, you cannot be sure that the in-memory state is synchronized. There are techniques to solve that, but they are rather complex.
As you don't describe the need for you to get the read model data immediately, it's hard to give specific advice, but I have some tips.
If you need it for the UI, and the UI needs the new entity state, you can return the entity state as the command handling result, as you already have it. Then, the UI can show the state immediately without executing any queries.
Same scenario, but you return a collection of new events to the UI. If the UI bit is built with something like React and Flux, they most probably already have "event sourcing" there (that's what Flux essentially is), and applying those events via their reducers they can update the UI without querying the read model.
If you know what read model needs to be in sync (I can't say how many you have), you can propagate the event commit position to the read model as a metadata property, or just as a document property. Then, you can hold the API call (basically wait) until the read model update position property gets equal to or more than the commit position. The drawback is that you can do it for a specific read model only, so your command handler needs to know too much about the read side.
Similar to (3) but you check the checkpoint store position. If the checkpoint store is not optimized with batching, it will soon pass over the last event commit position, then you return 200 OK to the caller. It's a bit easier than (3) as it only cares about the subscription checkpoint, not the single read model, but you need access to the checkpoint store.
The UI can do the same after they get the command handled, you need to return the commit position of the last event, and they query and wait.
I've seen all of the above working in production, but my preferred solutions are (1) and (2).
To make any of those work, your command service needs to return a sophisticated result to the caller (API, or beyond) as I've done in Eventuous.
QUESTION
I want to initialize tensor to sparse tensor.
When tensor's dimensional is 2, I can use torch.nn.init.sparse(tensor, sparsity=0.1)
ANSWER
Answered 2021-May-18 at 09:11This function is an implementation of the following method:
The best random initialization scheme we found was one of our own design, "sparse initialization". In this scheme we hard limit the number of non-zero incoming connection weights to each unit (we used 15 in our experiments) and set the biases to 0 (or 0.5 for tanh units).
- Deep learning via Hessian-free optimization - Martens, J. (2010).
The reason it is not supported for higher order tensors is because it maintains the same proportion of zeros in each column, and it is not clear which [subset of] dimensions this condition should be maintained across for higher order tensors.
You can implement this initialization strategy with dropout or an equivalent function e.g:
QUESTION
I am new to marten.
what is difference between IDocumentStore.OpenSession()
vs IDocumentStore.LightweightSession()
?
ANSWER
Answered 2021-May-03 at 07:37Based on the xml doc it is just a convenience method:
Convenience method to create a new "lightweight" IDocumentSession with no IdentityMap or automatic dirty checking
In the current implementation it just calls OpenSession
with DocumentTracking
set to DocumentTracking.None
.
Also from the troubleshooting docs:
From
IDocumentStore.OpenSession
Characteristics:
Defaults to session that tracks objects by their identity,
DocumentTracking.IdentityOnly
, with isolation level of Read Committed.Use: Reading & writing data. Objects within a session are cached by their identity. Updates to objects are explicitly controlled through session operations (
IDocumentSession.Update
,IDocumentSession.Store
). With the defaults, incurs lower overhead thanDirtyTrackedSession
.
And
From
IDocumentStore.LightweightSession
Characteristics:
No change tracking,
DocumentTracking.None
, with the default isolation level of Read Committed.Use: Reading & writing data. No caching of objects is done within a session, e.g. repeated loads using the same document identity yield separate objects, each hydrated from the database. In case of updates to such objects, the last object to be stored will overwrite any pending changes from previously stored objects of the same identity. Can incur lower overhead than tracked sessions.
QUESTION
I am trying to perform inner join on two vectors in rust but not sure how to achieve this.
In short, I am looking for employees with their department name.
If anybody is familiar with C# LINQ here, then I am trying to achieve something like below in rust.
Considering same model as specified below in model.rs
ANSWER
Answered 2020-Nov-28 at 16:16If you just want to get pairs of &str
for the names of the departments and the employees, you can use an iterator chain like so:
QUESTION
so I have an array in my code below but one of my requirements for the assignment is to have a very LARGE array of objects around like 10,000 objects. My teacher was saying that the computer can just keep generating random objects for you given how many you want so in my case like 10,000. I'm just confused about how I would do that, any help or suggestions are really appreciated thank you!
...ANSWER
Answered 2020-Oct-29 at 01:09That's a perfect job for a loop. You have to create helper functions that generate random names and prices and types.
For the name
, we'll use:
QUESTION
I have an ugly dataframe I inherited, like so:
...ANSWER
Answered 2020-Oct-20 at 19:29As I said, no merging required in this problem. Also, I would recommend using data.table
package to solve your problem, once it's simpler to perform modifications at specific rows based on conditions.
A solution using data.table
would be:
QUESTION
How would I match a name, such that one of the middle letters of the name must come from the word 'qwerty'(thus containing either of the letters 'q', 'w' , 'e', 'r', 't','y')?
I am curious how you can determine what the middle letters are, this would make use of some string count I assume.
What I have tried so far:
...ANSWER
Answered 2020-May-15 at 09:07You seem to want to match the same amount of chars on the left and right and then some chars in the middle, but this is not possible with PostgreSQL regex.
To find records that contain any of the characters in a pre-defined set, you may use SIMILAR TO
with a %[qwerty]%
pattern:
QUESTION
I'm on Masstransit 6.2.
I'm using Marten for saga storage and serilog for logging.
My saga often gets database concurrency exceptions but can be recovered using retry/re-delivery. However these exceptions are logged as "SAGA:" errors along with the "R-RETRY" warnings.
I found this old issue https://github.com/MassTransit/MassTransit/issues/626, apparently this has been addressed? Is there anything can be done to downgrade these errors or stop logging them?
...ANSWER
Answered 2020-Mar-17 at 06:24Confirmed this is fixed in 6.2.2.
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