Re: [pcp] RFC: allowing longer metric and instance names in MMV(5) format

[Ryan Doyle <ryan@xxxxxxxxxxxx>]

On 2016-06-29 15:35, Nathan Scott wrote:

> The fundamental problem is that the "on-disk" metric and instance
> types for MMV encode the names in a 64 byte character array.  So,
> I'm suggesting we support an optional (non-default) v2 MMV format
> which would be exactly the same as v1 except that metric/instance
> structures could specify the offset to a mmv_disk_string_t for the
> name (instead of embedding it directly).
+1

> If a metric/instance name is presented that is too large to fit in
> v1 format, the client library could transparently switch to using
> v2 format and continue on.
I wonder if the backwards compatibility is worth it? Seeing as we have
a version number in the header of the MMV, perhaps the expectation is
that if you are using V2, your instances, metrics and indoms are in
the correct format for that version (using the string offsets).

The MMV PMDA would of course be able to decode either version.

Thoughts?
Ryan