3 ms·

Just the temporal properties alone make it very useful for anything where it matters like billing, finance, inventory. Else you are in views/schema/indexing hel

by alecco 4y ago

Just the temporal properties alone make it very useful for anything where it matters like billing, finance, inventory. Else you are in views/schema/indexing hell to do it on top of SQL. There is some SQL temporal support but it's not great and varies a lot. Also since it's not native to the storage it has a lot of complexity issues under the rug making it not great. Many financial systems use Event Sourcing (OOP + ORM). I had to suffer this at a previous employer. See https://vvvvalvalval.github.io/posts/2018-11-12-datomic-event-sourcing-without-the-hassle.html https://vvvvalvalval.github.io/posts/2018-11-12-datomic-even...

slaymaker1907 4y ago
The temporal support seems handy, but time is still going to be really tricky for financial systems. Datomic only covers what the physical state of the database was at a particular time, but there's also the effective legal time (maybe a payment was dated a day before the system actually processed it) as well as requirements to remove data after a period of time (including point in time stuff).
- augustl 4y ago
  Indeed, it depends a lot on the domain. Datomic only has "technical" database time, and doesn't have any built-in way of modelling domain time. You can set the transaction timestamp manually when you write, but you can't set it to be earlier than the latest transaction that was committed. So, if you want your domain modelling to piggyback on Datomic time travelling, you can only do things like delaying writes for, say, an hour, and hope you have all the data by the time you commit to db.
- nlitened 4y ago
  There's a bitemporal Datomic-like database from JUXT that does exactly that, I believe https://www.xtdb.com https://www.xtdb.com
riku_iki 4y ago
> Just the temporal properties alone make it very useful for anything where it matters like billing, finance, inventory. you can easily create datamodel to have this in SQL dbs: create table transaction_history(..., execution_time timestamp);
- tasuki 4y ago
  This is not an answer, it's the beginning of a question. Yes sure, we know `create table` and we know it's a good idea to record the execution timestamp. What exactly do you put in the place of the three dots?
- augustl 4y ago
  Fyi, Datomic lets you look at the entire database at any point in time, as an immutable value. Also, you can annotate transactions with metadata, and query for "which tx wrote this specific value for this row/column" and look at custom metadata you added to the tx to reason about your system. Doing all of that in SQL is not trivial, to say the least.

by alecco 4y ago

slaymaker1907 4y ago

The temporal support seems handy, but time is still going to be really tricky for financial systems. Datomic only covers what the physical state of the database was at a particular time, but there's also the effective legal time (maybe a payment was dated a day before the system actually processed it) as well as requirements to remove data after a period of time (including point in time stuff).

augustl 4y ago
Indeed, it depends a lot on the domain. Datomic only has "technical" database time, and doesn't have any built-in way of modelling domain time. You can set the transaction timestamp manually when you write, but you can't set it to be earlier than the latest transaction that was committed. So, if you want your domain modelling to piggyback on Datomic time travelling, you can only do things like delaying writes for, say, an hour, and hope you have all the data by the time you commit to db.
nlitened 4y ago
There's a bitemporal Datomic-like database from JUXT that does exactly that, I believe https://www.xtdb.com https://www.xtdb.com

riku_iki 4y ago

> Just the temporal properties alone make it very useful for anything where it matters like billing, finance, inventory. you can easily create datamodel to have this in SQL dbs: create table transaction_history(..., execution_time timestamp);

tasuki 4y ago
This is not an answer, it's the beginning of a question. Yes sure, we know `create table` and we know it's a good idea to record the execution timestamp. What exactly do you put in the place of the three dots?
augustl 4y ago
Fyi, Datomic lets you look at the entire database at any point in time, as an immutable value. Also, you can annotate transactions with metadata, and query for "which tx wrote this specific value for this row/column" and look at custom metadata you added to the tx to reason about your system. Doing all of that in SQL is not trivial, to say the least.