Comment by Bolwin
18 days ago
Interesting, never heard of this before. I'm assuming the use case is when your data is too large to conveniently fit into memory?
18 days ago
Interesting, never heard of this before. I'm assuming the use case is when your data is too large to conveniently fit into memory?
It's a database for strictly exact-match lookups for very read-intensive workloads; think systems where the database only changes when the configuration changes, like email alias or domain lookups. It's very simple (a first-level hash table chaining to a second-level open-addressed hash table) and easy to get your head around, but also very limiting; an otherwise strict K-V system that uses b-trees instead of hash tables can do range queries, which you can build a lot of other stuff out of.
Most people would use Redis or SQLite today for what CDB was intended for; CDB will be faster, but for a lot of applications that speed improvement will be sub-threshold for users.
Great reply.
What comes to mind from my experience is storing full shipping rate tables for multiple shipping providers. Those change extremely rarely but are a high throughput exact lookup in a critical path (a checkout).
But we just implemented them in SQLite and deployed that file with the application. Simple clean, effective, and fast. Maybe shipping rate data is smaller than this is intended for, but I doubt using this instead would see a consequential perf increase. Seems niche, like the domain name lookup example.
For me this answer was helpful and succinct, thank you.
It is a database for when you read a lot and don't write too often; when a write might be pretty big but not frequent; when you don't want to write a database engine yourself (I.e. figure out what to write and when). And, especially, when corrupting the data would be a big problem.
And it is especially good on copy-on-write filesystems, because it is CoW itself.
So it's not constant?
The lookups are ~O(1).
Nothing is truly constant lookup in number of elements in nature because we can’t pack it tighter than a sphere.