Hi,
last year we published some work [1] about using IETF YANG-push for
telemetry streaming in the context of optical networks. One of the use
cases was continualy sending spectral scans, and for us that meant updating
a list of roughly 15-20k items at least once per second.
Think of this as a list of (frequency, power) pairs where the "frequency"
can be implied, so the data was really a "a long vector of numbers". We
were not able to use either `list` or a `leaf-list` directly for
performance reasons. The root cause is that `leaf-list` traditionally used
to be "an ordered set". It was changed to allow duplicate values in YANG
1.1, and that for ops data only. Still, various implementations try to look
at the operational leaf-lists and helpfully compute diffs, they look for
item moves, etc. This is not cheap for 15-20k items.
In the end we used a model like this:
leaf lowest-frequency {
type frequency-ghz;
config false;
mandatory true;
description "Lowest frequency slice in the `p` list.";
}
leaf step {
type frequency-ghz;
config false;
mandatory true;
description "Each subsequent `p` result is this far from the previous
one.";
}
anydata p {
config false;
description "Measured power. Sorted by frequency, starting at
`lowest-frequency`, step size `step`. Individual items are decimal64
numbers.";
}
The JSON-encoded data looked like this:
{
"something: {
"lowest-frequency": 123456,
"step": 1,
"p": ["0.003", "0.001", "0.001", "0.24", "0.37"]
}
}
Our internal implementation uses libyang, and we're now updating form
libyang v1 to libyang v2, which assumes that our `p` has to be encoded as
JSON object. This of course produces an invalid JSON:
"p": {["0.003", "0.001", "0.001", "0.24", "0.37"]}
I have a few questions:
- Can `anydata` represent a JSON array directly? On one hand the standard
says that "An anydata instance is encoded in the same way as a container,
i.e., as a name/object pair", but then it also allows the `empty` thing via
`[null]`. Or is it perhaps allowed only for *members* of this faux
container?
- In case `anydata` is not a good match, I suppose `anyxml` will work fine
because the example in the RFC is already using an array. Perhaps we could
also use JSON numbers directly without encoding as a string as well.
- Is there a better approach than this one? Can I reasonably expect "all
the YANG implementations out there" to stop looking at operational
leaf-lists as essentially ordered sets? I think the answer is "no", but I
am looking for suggestions.
With kind regards,
Jan
[1] https://ieeexplore.ieee.org/document/9457112
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