I was reading datomic’s tutorial on transacting schemas referenced here: https://docs.datomic.com/on-prem/getting-started/transact-schema.html

But I notice in other sites or examples, there are two additional attributes specified that are not in the tutorial: :db.install/_attribute and :db/id

Is there a reason those attributes are not presented in the tutorial?

@fuentesjr those used to be required, but now are not

the other examples you are seeing are older

are those attributes no longer necessary, or do they simply have default values that can be overriden?

the attributes are there, you just do not have to supply them

in every case db id should be tempid in :db.user/db partition and :db.install/_attribute should be :db.user/db

they just went from requiring them for installation to inferring them

(inferred from the presence of :db/type and :db/cardinality probably)

what those did was add the new attribute to the :db.user/db entity (entity id 0) on its :db.install/attribute attribute

now that happens without you asking for it

https://docs.datomic.com/on-prem/changes.html#0.9.5530

released 2016-11-28

so by default now all schemas are created in the db.part/user partition when those attributes are not specified?

Also, are the entity ids unique across all of the db or are they unique only within the partition they reside?

@fuentesjr I think so. It seems like partition control in general has fallen out of common practice. I'm not sure it's even possible in Datomic Cloud. I think I read somewhere that they found it wasn't being used much and may not be "worth its weight" in the API.

Not sure about your second question.

I'm pretty sure schema is still put in the db.part/db partition

interesting

this was mostly an interface change (you no longer need to include those assertions in your tx data) not a functionality change

if you look at the datoms added after the tx I am pretty sure they are the same

My understanding is that partitions are primarily a means of improving performance by controlling which of your datoms get indexed/cached "closer" to each other. I'm not sure if they have other functional/semantic implications.

they don't, but schema is supposed to go in db partition and I don;t think they changed that

practically speaking this just means that the entity id of attributes will be smaller

I see. So by looking at the presense of :db.type and/or :db/cardinality, they store those datoms in db.part/db otherwise … they store them in db.part/user

This "best practice" in the Datomic docs might need to be updated. https://docs.datomic.com/cloud/best.html#optimistic-concurrency I'm getting a java.util.concurrent.ExecutionException containing an ExceptionInfo with {:db/error :db.error/cas-failed}. Is that how to detect CAS failures now?