Max Datom: Interactive Datomic Tutorial

by tosh • 4 years ago

62 30 4 years ago

cdiamand• 4 years ago

Fun tutorial! When does it make sense to use Datomic over something like MySQL or PostgreSQL?

abraxas• 4 years ago

Mostly when you need a ledger like functionality to your data. Datomic preserves the history of all the changes by design so it is very easy to reconstruct the history of changes to your data.

If this describes the majority of your problem space then Datomic is a good fit. Otherwise I would stick to a popular RDBMS like Postgres to leverage the community behind it. You will have a much easier time interacting with a well understood open source engine.

emccue6• 4 years ago

I think this is true - you will have an easier time not blazing new trails in general - but the need of ledger-like functionality isn't the distinguishing factor.

Preserving the history of all changes isn't just for reconstructing that history later, it's a central component in maintaining ACID while allowing for distributed readers.

Datomic has a singular transactor - node that can accept writes. So all transactions happen in sequence and consistency is maintained within the data model.

So your database goes

DB (0 transactions) -> DB' (1 transaction committed) -> DB'' (2 transactions committed)

With normal databases, when DB'' is created, DB' is lost. You change stuff in place. This means that anyone wanting to observe a consistent view of the database needs to coordinate with writes. This is why SQL dbs are single giant machines.

For Cassandra, Dynamo, Mongo, etc you still change stuff in place, but you just accept that things will be potentially inconsistent ("eventually consistent") for your readers. Once you drop that part of ACID you can scale your readers and your writers arbitrarily.

With Datomic DB, DB', and DB'' are still maintained. If you want to read the database "now" you can get a handle to the state that your reader thinks is the most recent. This might not be behind the absolute newest state that the transactor knows about, but it is still a consistent view of the database.

Its because of this you can scale your read nodes independently of the system. Because if you are reading DB' you know the value of that won't change you can load chunks of the indexes into the memory for caching and even embed the querying into the application making queries.

The proprietary-ness and JVM-ness of Datomic are its biggest weaknesses. I choose to believe those weaknesses can be addressed.

john5674• 4 years ago

This is true but it's a false premise. You have history but it's clunky to work with.

You won't be able to "source" and recreate the past without some work and unexpected things will happen when you "source" the past with the most recent code.

It useful but the history aspect is easily misunderstood.

emccue6• 4 years ago

As the world stands today, it makes sense to use Datomic if you are writing code on the JVM and are willing to pay for the database and associated support.

In a hypothetical future world where the data model and query approaches have more widespread open source adoption it is competitive for a lot of the same use cases.

casion• 4 years ago

In addition to what was said, Datomic Cloud automates a lot of the annoying and difficult to suss deployment for application dev, not just the database. You can deploy large scalable apps in minutes and easily deploy new code in minutes with no down time (or architecting a deployment system yourself).

alecco• 4 years ago

Datomic is elegant and it has some interesting properties like temporal. This is a huge win for many cases where business logic needs them (e.g. finance). I think it would make more sense for clients also running JVM. I don't have much experience with it but it looks very good. -- a SQL engine dev

john5674• 4 years ago

What I've find most useful is the immutable nature of the database. That within a reactive framework for UX is great combination. You get really cool things to happen with little effort.

Also, because the database is a value. You can easily do mock data and isolated transactions locally to experiment and test. This makes some things easier.

Another cool thing is how you do cross database queries by simply passing multiple databases to a function. It will pull in the subset of the dataset needed to compute the query result. It's that easy to do.

It's not good at dealing with high volume transactions (a lot of writes) it's not too bad but it's not built for that primarily.

amelius• 4 years ago

What I've find most useful is the immutable nature of the database.

Not really a good fit for today's world of privacy regulations, where deletion of data should be possible and guaranteed.

emccue6• 4 years ago

If anyone is interested, I am attempting to revive an open source clone of Datomic called EVA.

As is the original codebase works fine, its just unmaintained. My hope is to clean up the code, make an HTTP layer for a remote peer, and make a Rust embedded peer so that this sort of Database can finally escape the JVM.

https://github.com/bowbahdoe/eva

If you want to use something open source today that has the same query language but a different data model, https://xtdb.com/ is high quality.

panick21_• 4 years ago

Oh really interesting. I didn't know about that. I was actually going threw the old Mendat code base and was considering using that.

I would really like a pure Rust version of Datomic for embed use cases.

There is all also Datahike, that is going in that direction too. It is maintained and actively developed.

https://github.com/replikativ/datahike

emccue6• 4 years ago

Feel free to reach out via any of the contact info on my github. The more the merrier chasing this magic dragon.

den1k• 4 years ago

if you don't need history, have a look at https://github.com/juji-io/datalevin

emccue6• 4 years ago

Datalevin is good, but its more useful in the same realm as sqlite

layer82• 4 years ago

“Your browser is not wide enough to properly render MaxDatom”

Okay.

LesZedCB• 4 years ago

its a game kinda thing. it needs rendering space. not mobile friendly

layer82• 4 years ago

It would be helpful if they’d say how wide it needs to be (landscape didn’t help) or that it doesn’t work on mobile.

icosahedron3• 4 years ago

Can anyone else get beyond the 2nd level? I am getting stuck because it returns the values in slightly different order than is expected. And I don't see a way to report an issue via the website.

icosahedron3• 4 years ago

I was able to use find the author on the title page, and emailed them. I don't know if my query is incorrect or if it's a bug.

icosahedron3• 4 years ago

Ha, as is often the case, I was making things more complicated than necessary. Jarrod got back to me quickly and let me know the err of my ways. :D

Max Datom: Interactive Datomic Tutorial

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