Why not supply async api in mongo C driver?

kuku_super · 2021-02-20T10:54:25.150Z

async api would be more effective, and less threads. why not supply in mongo c driver?

there are async api in mongo java driver

Kevin_Albertson · 2021-02-24T15:18:32.815Z

Hi @kuku_super, thanks for reaching out!

An async API on the C driver has been considered before. It is not outside the realm of possibility. Notably, the investigation in CDRIVER-27 concluded the current multi-threaded API could maintain throughput well as the number of application threads increased.

Do you have a use case in mind for an async API? Has the number of threads spawned by libmongoc been problematic?

Sincerely,
Kevin

kuku_super · 2021-03-08T02:54:04.248Z

Hi @Kevin_Albertson , thx for ur reply.

if changed the request waits 0 - 2 ms, then we compared the thread pool solution and the async solution with 1 cpu. the async solution would give more qps, more than 20% better.

more quickly the request, there would be more context switch.

kuku_super · 2021-03-28T09:23:39.093Z

hi, @Kevin_Albertson, give a use case in game server.

we service 10k player in a server process with only one cpu. every player would save data to mongodb once 1 second. so , there would be 10k qps ops. suppose 10ms per op, if we use thread pool solution, we need 1000 threads only one cpu. we would deploy 5-6 processes on one server with 8 cpus. the context switch would cost too much cpu.

so async solution would be better.

would async solution be considered again?

look forward to your reply , @Kevin_Albertson.

marty1885 · 2021-08-15T00:58:28.769Z

Hi, sorry for bumping the thread.

I’m a maintainer of drogon framework. We’ve investigated MongoDB support a while ago. But stopped by the fact that the C API does not support async mode. The main reason being we want to keep the high concurrency all time in our framework and reduce context switches. From our experience, running DB on the same thread as the HTTP request can improve throughput up to 20%. And we try hard to keep all threads not blocked under all circumstances. Otherwise performance tuning becoming a loose-loose game of balancing number of DB threads and dealing with the drawbacks of having too many threads.

Hopefully the feedback can push this forward.

Michael_El_Baki · 2022-11-07T17:45:35.203Z

Hello, just bumping this thread again. Are there some news here? Really surprised that the C driver has no async feature. Still nothing planned in a near future? As has been mentioned earlier, in a high concurrency context like can be for some web services, async model usually performs a lot better than managing a high number of threads. I would be worried to begin my developments with a sync model…
@kuku_super @marty1885 do you have any feedback that you can share when using sync model with threads?
Thanks a lot!

Arran_Cudbard-Bell · 2023-08-11T21:24:29.855Z

Our application uses one worker thread per CPU core present on the system, with an interpreter which allows coroutinelike/greenthreadlike behaviour. On I/O that would block, the current request yields control back to the interpreter which services other requests whilst waiting for a response. With this model, blocking I/O introduces severe reliability issues where if a worker thread is blocked, its input queues are quickly overwhelmed and we start dropping packets. The only way we can work around this, is to have a pool of threads dedicated to performing blocking I/O. This introduces a significant performance penalty, and greatly increases code complexity. Supporting async I/O isn’t just about performance, it’s required when working within an event driven programming paradigm.

Rishabh_Bisht · 2023-08-14T09:06:14.030Z

Hi all,

I am the Product Manager for C/C++ drivers and developer experience. I wanted to take a moment to express my gratitude for everyone’s active participation and feedback in this discussion.

We understand the importance of async/event driven paradigms in modern software development, and are committed to continuously improving our offerings to better meet the evolving needs of our users.

Your inputs help us prioritise our efforts and align our roadmap with the features and enhancements that matter most to you. Rest assured, we are actively monitoring the feedback and votes on this suggestion, and your voice will play a significant role in shaping the future direction of our MongoDB C Driver.

I’d highly encourage to cast your votes on the MongoDB Feedback Forum for this request - Asynchronous variant of MongoDB C Driver – MongoDB Feedback Engine .

-Rishabh

Rishabh_Bisht · 2025-03-12T10:44:00.351Z

Hi all, I am excited to announce the release of amongoc - an asynchronous C driver for MongoDB, now in public preview. This experimental driver aims to provide an efficient, non-blocking interface for MongoDB operations.

Share your feedback on GitHub to help shape its development into a production-ready tool. Your input is crucial, and we can’t wait to see what you’ll build with amongoc!

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