datomic 2018-02-25 | Slack Archive

stuarthalloway14:02:26

@captaingrover in general, whenever your system’s behavior does not match your expectations, I would recommend the scientific method https://www.youtube.com/watch?v=FihU5JxmnBg

Desmond21:02:26

@U072WS7PE Yeah, I wound up finding a couple of issues besides the n+1 just by removing different parts of the query and timing the result from the repl. For example, I was joining across attributes that were not :db/id & :db.type/ref. I probably should have know that would be slow but seeing the numbers makes it a lot more real. Good talk! Thank you!

stuarthalloway14:02:58

that said, you can also improve your expectations in advance by creating SLAs, by modeling your system, and by generative and simulation testing

stuarthalloway14:02:41

in your specific example, testing with simulated load would certainly uncover any n+1 roundtrip problem in a system

Drew Verlee20:02:55

Watching the day of datomic video’s i’m somewhat confused by how were using Ids in the transaction to refer to other entities. https://vimeo.com/208663465#t=600s here is the code that stuart is referring to:

[{:person/name "bob"}
 {:person/id  "a"
  :person/name "Alice"
  :person/spouse "b"}]

Here i would assume what he is describing is how we can transact the idea that bob is married to alice without yet having an id for bob. i would expect that to look something like:

[{:person/name "bob"
  :db/id "b"}

{:person/name "Alice"
:person/spouse "b"}]

potetm20:02:41

@drewverlee I’m pretty sure you’re correct. Either that’s a typo or datomic is inferring from the fact that there are no other entities in the transaction.

potetm20:02:51

I’ve not tried it, but what you have is what I would do.

Drew Verlee20:02:44

Thanks @potetm. I assuming the schema also says that person/spouse is a ref. Also these docs on creating tempIds seem to indicate that the above (as i wrote it at least) would work: https://docs.datomic.com/on-prem/transactions.html#creating-temp-id

Drew Verlee21:02:10

(let [schema {:aka {:db/cardinality :db.cardinality/many}}
             conn   (d/create-conn schema)])

a shorthand for {ident {shema-key shema-value}} as opposed to: (schema [{:db/ident :aka, etc…}]

2018-02-25

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