[leokennis]

We (as in, my company, not me myself) run large Cassandra clusters in the critical path of bank transaction processing (in the order of 2-25 million payments per day, each requiring a lot of database queries) and it's going pretty well...

https://www.youtube.com/watch?v=0QsLU9na2uE

But yes, you win some (mainly resilience, availability and disaster avoidance, possibly tunable consistency will help you) you lose some.

[hsjqllzlfkf]

To do 2-25 million transactions per day you might as well use SQLite. Sounds like this was a career development push more than anything.

[leokennis]

Transaction in this case is not a database transaction, but a financial transaction (payment). Per payment, probably somewhere in the order of 50-100 database transactions (although Cassandra does not really have transactions of course, interpret this as read/write actions) will be performed in the course of its processing. So that is 1,875,000,000,000 database actions on busy days. Not a DBA, but for our purposes the scalability and availability of Cassandra works very well.

[giovannibonetti]

There are three extra zeros here

[leokennis]

Whoops you are right.

[stubish]

There is always a better solution than Cassandra, until your data will no longer fit on a single server or you actually need guaranteed availability.

[Alifatisk]

Is there no other db that offers guaranteed availability?

I remember reading about Discord switching from Cassandra to ScyllaDB I think.

[stubish]

Yes, other distributed databases like MongoDB, CockroachDB, probably a few others. Or even multi-master DB setups. As with Cassandra, you don't want to use them unless you really need that availability and can suffer the downsides. It seems pretty rare to actually need those availability guarantees, rather than say a robust fast failover setup which might cancel some in flight transactions. It is probably when you start looking at two phase commit that you look for alternatives with better availability stories.

[brianwawok]

ScyllaDB Is just knock off cassandra with different features and performance characteristics.

[mrweasel]

25 million per day might be a little high for SQLite, especially if they don't spread out evenly over the day. You also get no redundancy or replication, which you might want if your database isn't to grind to a halt during backups.

Arguably Cassandra does sound like a weird choice, but we don't know the specifics of their setup. There's a lot of solutions presented on HN where SQLite and a Java application would have been a better choice and you can say for sure without knowing all the details, I feel like this is past that point.

[hobs]

No need to add the extra bit - at the top end 289 transactions per seconds is not something you'd probably want to choose SQLite for, but PG/MySQL/SQL Server would do that fine and require a lot less feeding (though any database with traffic or size needs some care.)