chunked remote read: sending multiple series per frame?

[Tristan Su]

hi,

I'm trying to implement a remote read server and got a question regarding chunked response. 

From following comments:

https://github.com/prometheus/prometheus/blob/a6600f564e3c483cc820bae6c7a551db701a22b3/storage/remote/codec.go#L216

which says:

// Send at most one series per frame; series may be split over multiple frames according to maxBytesInFrame.

Is this a protocol constraint to not allow sending multiple series per frame? Or anything else I'm missing?

Thanks in advance,

Tristan

[Bartłomiej Płotka]

Hi Tristian,

That's correct. It will send at max 1 series per frame, even if small.

Kind Regards,

Bartek

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[Tristan Su]

Bartek,

Thanks for your quick reply. Could you share some background for this constraint?
To me it seems each `ChunkedSeries` has labels so a `ChunkedReadResponse` with different series is not a problem.  I may be missing something but just wondering...

Tristan

[Bartłomiej Płotka]

Correct, it's not a problem. However, still, the implementation and API guarantees that. We are kind of prepared for flexibility here in future, but I think we will need to version, or negotiate this etc.

All should be documented here: https://github.com/prometheus/prometheus/blob/38d32e06862f6b72700f67043ce574508b5697f0/prompb/remote.proto#L77

Particularly: "We strictly stream full series after series, optionally split by time."

And because of this e.g Thanos expects single series only: https://github.com/thanos-io/thanos/blob/c733564d44745af1a023bfa5d51d6d205404dc82/pkg/store/prometheus.go#L294

Hope that helps! 🤗

Kind Regards,

Bartek

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[Tristan Su]

fair enough. Thanks!