Unexpected behavior of aggregators

[sblatnick]

I've tried aggregate the metrics via 1 hour intervals:

And I would expect (like doing a LEFT JOIN in SQL), that any hours without any data will assume zero/null:

Or instead skipped points:

But instead, I see the points connected skipping the hour:

A major problem is, it appears during that hour, there was a value of 3, especially if you have a lot of data and don't show the points but just the lines.

I know I can get around this by submitting 0 data values for every group hourly, but that increases the data I need to submit and has the side effect of when a group leaves or has no activity for a period, then it would create a lot more lines all at 0. By supporting this option:

• It would be easier in the data submission
• The timeframe would only show active groups like it does now, with no need to keep track of which ones to send over 0 results for.

I hope this all makes sense. If I should file this elsewhere, let me know.

Notes:

• I used libreoffice to illustrate what I was seeing vs what I expected for simplicity.
• This may be a problem in kairosdb's query language, or it could be argued to add an option for this in the grafana UI. I've discussed this with some people, and they argue the first sample is kinda inserting points that isn't there, so perhaps the second one where the line is not continuous is better. Or perhaps this could be configurable in the options too.

[jifwin]

Hi This is very misleading. Unfortunately it is caused by KairosDB design. When there are no values in given time window KairosDB will return nothing, instead of null (or 0 for sum). Nulls would be very helpful, since we have a nice "nulls as zero" option in Grafana. I would try discussing that in: https://github.com/kairosdb/kairosdb

[sblatnick]

I filed https://github.com/kairosdb/kairosdb/issues/359 now. Thanks.