[ac130kz]

From what I looked at in the past, they seem better on paper by comparing themselves to a very old version of Redis in a rigged scenario (no clustering or multithreading applied despite Drangonfly getting multithreading enabled), and they are a lot worse in terms of code updates. Maybe that's different today, but I'm more keen on using Valkey.

[hp77]

Does Redis support multithreading? Doesn't it use a single-threaded event loop, while DragonflyDB basic version is with multithreading enabled and shared-nothing architecture. Also I found this latest comparison between Valkey and DragonflyDB : https://www.dragonflydb.io/blog/dragonfly-vs-valkey-benchmar...

[romange]

Valkey/Redis support offloading of io processing to special I/O threads.

Their goal is to unload the "main" thread from performing i/o related tasks like socket reading and parsing, so it could only spend its precious time on datastore operations. This creates an asymmetrical architecture with I/O threads scaling to any number of CPUs, but the main thread is the only one that touches the hashtable and its entries. It helps a lot in cases where datastore operations are relatively lightweight, like SET/GET with short string values, but its impact will be insignificant for CPU heavy operations like lua EVALs, sorted sets, lists, MGET/MSET etc.

[ac130kz]

IO multithreading is still not fully there, there were significant improvements within the first couple of iterations, hopefully, it will improve further. I see that Dragonfly uses iouring, which is not recommended by Google due to security vulnerabilities.

[romange]

Dragonfly supports both epoll and iouring, and polling engine choice is quite orthogonal to its shared nothing architecture. I do not think that Valkey or Redis will become fully multi-threaded any time soon - as such change will require building something like Dragonfly (or use locks that historically were a big NO for Redis).

(Author of Dragonfly here)

[hp77]

I read Google is limitting the use of io_uring, but I have seen io_uring being used in other Databases, TigerBeetle is another DB which uses io_uring.

[jorangreef]

Joran from TigerBeetle here.

Yes, per [1] Google did restrict their use of io_uring on “production servers“, and in Android, ChromeOS etc.

However, within that same post, and what is often missed when that post is quoted, is that Google wrote that they did in fact “consider [io_uring] safe” for use by trusted components:

> For these reasons, we currently consider it safe only for use by trusted components.

A database like TigerBeetle is typically deployed in a trusted environment, and is such a trusted component.

[1] https://security.googleblog.com/2023/06/learnings-from-kctf-...