Until I know, Whastapp dont save the messages in their database, just the accounts, the messages are peer to peer (I’m not sure, but its seems works like this)
WolfDan
jeramyRR
No, they save messages in Mnesia as well. You can send instant messages to people who aren’t online. Once they sign in it will pop them from the db. If I remember correctly I think I saw a talk where they stated the average amount of time a message remained in the db was about 27 minutes.
2
andre1sk
I think that’s not enough
I would at least add Kafka, Spark, Hadoop, Nifi, NATS, K8s, and Terraform
I would also roll my own implementation of viewstamped replication 
I obviously forgot a few things but for initial roll out this should be OK
2
andre1sk
Dude PG is not web scale. For just 100K a month you can have a Spanner setup that will easily match a single mid size PG box in performance.
2
technomage
We are getting very good results with Risk and its integrated SOLR search functions. There is a small delay while SOLR indexes update to the Risk database, but otherwise very scaleable with multiple writers and readers. It really depends on how complex your data model is, and how much traffic you expect. PG will be fine for anything under 1k simultaneous users for sure, and can go higher with effort.
0
braynm
I am interested to this as well, is using GenServer and persists the data to postgres enough?
0
idi527
Just a note about using mnesia in 201* https://news.ycombinator.com/item?id=10388488
It might have been an ok decision on whatsapp’s part in 2008, but now there are plenty of much better alternatives, I think. Myself, I would look at what discord guys are using, since they are also doing quite well.
Also, if you watch Rick Reed’s talk from 2012 or 2014, it would seem that mnesia was quite a big pain point for them even back then. I honestly think some of their problems could have been avoided if they had used something like cassandra. Instagram’s team used it well for their little chat.
0
idi527
marcuslankenau
I would think about the use cases you want to implement:
- how import is the chat history (if not at all I would just keep it in genserver)
- how long to you want to save the history
- how do you work the historical data afterwards (searching, scrolling)
- how big will the history get
- how many users
- how can you partition stuff (maybe there are groups that can be separated for easy charding)
When you know more about the use cases, the amount and the frequencies you can think about the technology.
If you want to get started quickly I would just use what you have, like postgresql and separate the storage from the core app. Then change to something more powerful when needed.
Marcus
0