[feature request] Optimize RAM usage of Microsoft Devices SDK

[taraspaliy]

We use Devices SDK v.1.32.0 (https://github.com/Azure/azure-iot-sdk-csharp/releases/tag/2020-10-15) for connecting with Microsoft IoT Hub on the low-end edge device armel based device with limited RAM.

In our solution we use Microsoft IoT Hub SDK for secure MQTT / Websockets connectivity with our cloud. Currently we are experiencing a high RAM usage by IoT Hub SDK libraries, especially for ensuring the secured connection. Using a profiler we found that the certificate manager class uses around 60MB of RAM. Also, an important note is that most of these 60MB are unmanaged memory that can't be cleared by GC.

Can you please advise on optimizing RAM usage of Microsoft IoT Hub SDK libraries? Also please let us know if there are some more light-weight versions of Microsoft libraries for IoT Hub related features.

[drwill-ms]

I'm afraid there is not another lightweight option to offer.

We can try to find time to do a thorough analysis of object lifetime and frugality of memory. Unfortunately, this code base supports many customers and we cannot make breaking changes, so that will limit us to some degree.

In the interest of finding some quick wins, if you'd share your profile results with us, we'd be happy to look at the top offenders. You mentioned a certificate manager class, but I don't find one by that name. Can you refer me to the specific file?

[az-iot-builder-01]

@taraspaliy, thank you for your contribution to our open-sourced project! Please help us improve by filling out this 2-minute customer satisfaction survey

[drwill-ms]

I didn't want this issue to be closed, just because I associated 1 PR with it that was merged.

[sharmasejal]

Hey @taraspaliy
We recently checked in a fix (linked here) which might've improved the memory management. Could you advice us on what your RAM requirement is?

[taraspaliy]

Hi @drwill-ms , @sharmasejal
Many thanks for your support and follow up on this.
At the moment our application consumes ~65MB and the target is to reach 40MB.
We will check internally the impact of this change on the RAM. I will keep you posted.

[drwill-ms]

@taraspaliy I don't know for sure if the change I made was the one requested, but based on the description it seems about right. It was holding a HashSet of all the thumbprints in the personal cert store in a static field on a static class which was only used during initialization. In your initial report it was mentioned that used 60MB of RAM, although it seems that would entirely depend on how many certificates were installed on your local system and it would take an awful lot of certificates' thumbprints to reach 60MB, so I do worry I didn't get the specific issue reported.

We haven't released a new version yet with this change. If you are able to validate by doing a local build, that's great. Otherwise let me know and I'll inform you here when a new version with this change is available.

[taraspaliy]

@drwill-ms Thanks for your support and for explanation. At least we can try and see what is the result. Would it be possible to get an unofficial build from CI/CD? There are too many dependancies so we have issues with building the solution

[drwill-ms]

I can provide a private drop to you over email. Send me your details to email you at <redacted>

[drwill-ms]

@taraspaliy we've published a release of our latest, including the specific fix I made. The details of version numbers and changes can be found at https://github.com/Azure/azure-iot-sdk-csharp/releases/tag/2021-01-21.

[drwill-ms]

I'm going to close this issue, as it has been a while since I've heard from you, but please do check out the latest release and LMK if you find any specific issues you'd like addressed.