> What's the overhead of using FUSE to implement LiteFS?
It's a tricky question to answer. Most of the noticeable overhead is on the write side. Initial benchmarks of overhead that I've seen locally are about 250µs for the write(2) and fsync(2) calls. It's closer to 100µs for read(2) calls. There are additional writes made behind the scenes as well for storing in a replication format for the other nodes too.
However, on the read side some of that is moot. For many databases, most reads will be in the OS page cache and a fetch from there seems to be closer to 4µs. If you're running a moderately sized database (e.g 1GB) on even a modest VM (e.g. 256 RAM) then most of your hot pages will be in the OS page cache so you shouldn't notice much overhead on the read side.
LiteFS is targeted at read-heavy workloads. If you need high write throughput of thousands of writes per second then LiteFS probably isn't a good fit.
> Is there an issue with OS compatibility?
LiteFS is Linux right now. We'll be supporting other operating systems via a SQLite VFS extension in the future. macOS has poor FUSE support right now and I'm not sure where Windows and BSD stand with their support for FUSE or FUSE-like systems.
FUSE is a better developer experience since the end user doesn't have to worry about loading the extension every time they use a SQLite driver or the sqlite3 CLI. LiteFS runs an HTTP API server to communicate between nodes as well and if you run multiple processes with a VFS then you have to determine which one should start up that server. Those are the main advantages. Otherwise they're similar file system level interfaces.
> FUSE is a better developer experience since the end user doesn't have to worry about loading the extension every time they use a SQLite driver or the sqlite3 CLI.
For the CLI that's a fair concern, but from an "I'm writing an application that links against libsqlite3 and/or includes sqlite3.c" I feel like the opposite is true: I'll have a much easier time configuring the VFS in my app than fiddling with FUSE mounts.
> LiteFS runs an HTTP API server to communicate between nodes as well and if you run multiple processes with a VFS then you have to determine which one should start up that server.
Wouldn't that be a similar problem as working out which process should be the writer? I'm admittedly not too familiar with either Litestream or LiteFS, so that might be a dumb question.
Is there an issue with OS compatibility? FUSE tends to require OS hooks, last I checked, and that can be somewhat hairy to deal with.