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---
title: "Datomic on global: good reasons for and against it"
date: 2020-10-22
layout: slides
lang: en
ref: datomic-on-global-good-reasons-for-and-against-it
published: false
---
# Datomic on global
**Good** reasons for and against it
---
# Premise
Datomic's bottleneck is **write** throughput, not read
---
When creating a new service...
---
```clojure
(defn database-for-service
[service]
(let [prototype (prototype-for-service service)]
(if (= :global prototype)
:datomic
#{:dynamodb :redis :nothing})))
```
---
...which is, in my opinion, a poor heuristic.
---
The deciding factor shouldn't be the prototype, but the **cardinality**
---
```diff
(defn database-for-service
[service]
- (let [prototype (prototype-for-service service)]
- (if (= :global prototype)
- :datomic
- #{:dynamodb :redis :nothing})))
+ (let [cardinality (cardinality-for-service service)]
+ (if (= :too-high cardinality)
+ #{:dynamodb :redis :nothing
+ :datomic))))
```
---
```clojue
(defn database-for-service
[service]
(let [cardinality (cardinality-for-service service)]
(if (= :too-high cardinality)
#{:dynamodb :redis :nothing
:datomic))))
```
---
But how to determine when the cardinality is
**`:too-high`**?
---
Let's think about the cardinality of existing services we know
---
What is the cardinality of...
---
# savings-accounts
---
# inductor
---
# crebito
---
# diablo
---
# lost-boy?
---
# hook?
---
# ledger
---
# blackleach
---
# notification
---
# toasty
---
# auth
---
# waypoint
---
# jurassic-park
---
Compare the database choice of services with similar cardinalities:
## notifications vs toasty
---
Compare different cardinalities for services on global prototype:
## jurassic-park vs auth
---
Compare different cardinality for different services inside the same domain:
## savings-accounts -> blackleach -> diablo -> ledger
---
## Thank you!
References:
1. these slides: [{{ site.tld }}/slides.html]({% link slides.md %})
2. [prose version of this presentation]({% link _articles/2020-10-22-datomic-on-global-good-reasons-for-and-against-it.md %})
3. "[Understanding Database Sharding](https://www.digitalocean.com/community/tutorials/understanding-database-sharding)"
|
