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0 pointskouteiheika5y ago0 comments

> No SQL database is the one thing I disagree with.

I'm not saying this approach is a good idea in every case. There are many situations where I would use a proper database. It really depends on what kind of app you're building, what kind of queries you want to run, how big is your dataset, your failover and availability requirements, your programming language, etc.

In my case it was a great decision. The code is simple, and the data is convenient to access since it is already packed in native data structures. And it's really, really fast since all of the "queries" are basically LLVM-optimized machine code.

> What if you want to write a SQL query/report?

I just write a few lines of normal Rust code to do that. Sure, it's not as convenient. But I don't need to do that as often, so I don't care.

> Do you have transactions?

The concept of 'transaction' doesn't really make sense in this approach, since I'm directly modifying the data in memory, every change I make is atomic and can't fail, and I flush the data to the disk atomically as well.

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4 comments · 1 top-level

jolux5y ago· 3 in thread

>The concept of 'transaction' doesn't really make sense in this approach, since I'm directly modifying the data in memory, every change I make is atomic and can't fail, and I flush the data to the disk atomically as well.

So you don't have mutable data shared between threads then?

kouteiheikaOP5y ago

> So you don't have mutable data shared between threads then?

I might have worded that one sentence a little better, sorry.

I do technically need to share data between threads, since my event loop runs on multiple threads, so if I want to mutably modify something I do need to wrap it either in a `Mutex` or an `RwLock` and lock it.

What I meant was that it is not the same as a "transaction" in the SQL sense. It can't fail, there is no rollback, I decide on my own what level of granularity I need, and I bake the necessary atomicity into the data structures itself. So there are no SQL-style transactions anywhere - I just use a lock where it's appropriate to directly modify the memory, just as you'd do in any other situation. (Either by wrapping the whole structure in a lock, or wrapping only a single field, or by simply making the field atomic by itself.)

tinco5y ago

So it's a simple mmap database like early versions of MongoDB? I like using atomic commands, but I imagine it would become tedious fast to do the extra work of doing the accounting of the transaction manually every time you want to do a non atomic transaction.

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pastage5y ago

The basic stuff Rust will solve for you, but it is easy to forget logical dependencies and get an inconsistent state anyways... Just the ordinary close a session, send error message if not alive has bitten us in a 20 person project.

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