Native async implementation

[Archmonger]

python-diskcache currently relies on the built-in sqlite library in order to function. It would be relatively simple to duplicate the current API into an async version. This will result in much higher theoretical performance in high-utilization scenarios.

In theory, the current API could be perfectly replicated as async. For example, with __getitem__...

class AsyncCache:
    async def __getitem__(self, __name: str):
        ...

async def test():
    cache = AsyncCache()  # non-functional example
    await cache["abc"]

I would recommend using aiosqlite for this. It likely will need to be an optional dependency.

pip install diskcache[async]

I would recommend validating whether or not aiosqlite is installed during the __init__ of AsyncDiskCache. Throwing an error like this seems reasonable: AsyncCache requires the aiosqlite dependency.

Adding support for async within DjangoCache would require creating a* methods, such as adelete, aset, etc.

[grantjenks]

A few thoughts:

1. aiosqlite doesn’t implement a real async layer atop SQLite. Instead, it just uses threads: https://github.com/omnilib/aiosqlite/blob/main/aiosqlite/core.py#L76 The same pattern can be done with DiskCache and threads already. Just use the run_in_executor api provided by the built-in asyncio. I would expect lower utilization due to the additional threading layer overhead.

2. I don’t want to duplicate all the methods in DiskCache just to prefix the letter “a” to the methods and sprinkle the “async” keyword everywhere. I understand it’s maybe a simple source transformation but it seems burdensome from a maintenance perspective. I wish there was some way to make the same method “optionally” async.

3. Because SQLite runs in-process, even if there were a native async-friendly driver layer, what would it await? There’s no network call as there is with separate server databases like Postgres or MySQL. There’s a disk call deep inside the SQLite code but I don’t think the SQLite api exposes an async api for interacting at that low level. I don’t think Python supports async for disk reads/writes in the standard library either.

4. If it’s just the async Django cache methods that you’d like to use then the run_in_executor trick should work fine there. DiskCache needs to be updated for the Django 4.2 release too.