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heatmap: Docs and heatmap fixes

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Torkel Ödegaard
2017-05-11 10:19:47 +02:00
parent 30b6c3b54a
commit ab6740c685
5 changed files with 57 additions and 58 deletions
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docs/sources/features/panels/heatmap.md
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@@ -20,7 +20,7 @@ The Heatmap panel allows you to view histograms over time.
A histogram is a graphical representation of the distribution of numerical data. You group values into buckets
(some times also called bins) and then count how many values fall into each bucket. Instead
of graphing the actual values you then graph the buckets. Each each bar represents a bucket
of graphing the actual values you then graph the buckets. Each bar represents a bucket
and the bar height represents the frequency (i.e. count) of values that fell into that bucket's interval.
Example Histogram:
@@ -34,9 +34,9 @@ this is where heatmaps become useful.
## Heatmap
A Heatmap is like a histogram but over time where each time slice represents it's own
histogram. Instead of using bar hight as a represenation of frequency you use a cells and color
the cell propotional to the number of values in the bucket.
A Heatmap is like a histogram but over time where each time slice represents its own
histogram. Instead of using bar height as a representation of frequency you use cells and color
the cell proportional to the number of values in the bucket.
Example:
@@ -64,8 +64,7 @@ the time range `1h`. This will make the cells 1h wide on the X-axis.
### Pre-bucketed data
If you have a data that is already organized into buckets you can use the `Time series buckets` data format. This
format requires that your metric query return regular time series and that each time series has numeric name
If you have a data that is already organized into buckets you can use the `Time series buckets` data format. This format requires that your metric query return regular time series and that each time series has a numeric name
that represent the upper or lower bound of the interval.
The only data source that supports histograms over time is Elasticsearch. You do this by adding a *Histogram*
@@ -77,7 +76,30 @@ You control the size of the buckets using the Histogram interval (Y-Axis) and th
## Display Options
The color spectrum controls what value get's assigned what color. The left most color on the
spectrum represents the low frequency and the color on the right most side represents the max frequency.
Most color schemes are automatically inverted when using the light theme.
In the heatmap *Display* tab you define how the cells are rendered and what color they are assigned.
### Color Mode & Spectrum
{{< imgbox max-width="40%" img="/img/docs/v43/heatmap_scheme.png" caption="Color spectrum" >}}
The color spectrum controls the mapping between value count (in each bucket) and the color assigned to each bucket.
The left most color on the spectrum represents the minimum count and the color on the right most side represents the
maximum count. Some color schemes are automatically inverted when using the light theme.
You can also change the color mode to `Opacity`. In this case, the color will not change but the amount of opacity will
change with the bucket count.
## Raw data vs aggregated
If you use the heatmap with regular time series data (not pre-bucketed). Then it's important to keep in mind that your data
is often already by aggregated by your time series backend. Most time series queries do not return raw sample data
but include a group by time interval or maxDataPoints limit coupled with an aggregation function (usually average).
This all depends on the time range of your query of course. But the important point is to know that the Histogram bucketing
that Grafana performs may be done on already aggregated and averaged data. To get more accurate heatmaps it is better
to do the bucketing during metric collection or store the data in Elasticsearch, which currently is the only data source
data supports doing Histogram bucketing on the raw data.
If you remove or lower the group by time (or raise maxDataPoints) in your query to return more data points your heatmap will be
more accurate but this can also be very CPU & Memory taxing for your browser and could cause hangs and crashes if the number of
data points becomes unreasonably large.