Can UMA log negative samples?

[Chris Mumford]

Can UMA log negative samples? From what I can see only UMA_HISTOGRAM_SPARSE_SLOWLY can log negative values.

[Scott Hess]

On Wed, Jan 18, 2017 at 11:17 AM, Chris Mumford <cmum...@chromium.org> wrote:
> Can UMA log negative samples? From what I can see only
> UMA_HISTOGRAM_SPARSE_SLOWLY can log negative values.

Non-sparse logs to buckets in an array, and the array is pushed up (so
you should only use a dense set of small positive integers). Sparse
logs to a hash, so you can log sparse values, but best to not log
~tons of sparse values.

HistogramBase::Sample is int32_t, SampleMap uses a
std::map<Sample,Count>, so I expect things are probably safe-ish on
the client side. But I'd go looking for examples with negative values
on the UMA server before landing anything, just in case.

-scott

[Alexei Svitkine]

Yeah, it's currently not supported except for sparse - which is just meant for enum-like data (e.g. error codes).

One workaround is to define a separate histogram for negative values and log the negate the values logged there.

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[Chris Mumford]

Thx Alexel

[Vincent Scheib]

I wondered/looked for this a bit back as well. I thought a solution would be to have code shift values into the positive integer range [0,whatever], and then in the UMA tool remap them back to the meaningful range.

So, feature request for a units annotation that maps how values are displayed?

On Wed, Jan 18, 2017 at 11:55 AM, Chris Mumford <cmum...@chromium.org> wrote:

Thx Alexel

[Alexei Svitkine]

I think the data format should already support arbitrary bucket ranges (including negatives).

I think all that's needed is to make the base/metrics Histogram classes support it.