to_metrics_histogram now collapses duplicate integer bucket bounds
caused by Min less than Precision scaling while always keeping native
histogram metadata.
Signed-off-by: Amnon Heiman <amnon@scylladb.com>
Previously, histogram sums were estimated by multiplying bucket offsets
by their counts, which produces inaccurate results - typically too high
when using upper limits or too low when using lower limits.
This patch adds accurate sum tracking to approx_exponential_histogram:
- Adds a _sum member variable to track the actual sum of all values
- Implements sum() method to return the accumulated total
- Updates add() to increment _sum for each value
- Modifies to_metrics_histogram() helper to use the new sum() method
This change is important as histograms will be used instead of counters for
byte statistics, where accurate totals are essential for metrics reporting.
Signed-off-by: Amnon Heiman <amnon@scylladb.com>
approx_exponential_histogram uses similar logic to Prometheus native
histogram, to allow Prometheus sending its data in a native histogram
format it needs to report schema and min id (id of the first bucket).
This patch update to_metrics_histogram to set those optional parameters,
leaving it to the Prometheus to decide in what format the histogram will
be reported.
Signed-off-by: Amnon Heiman <amnon@scylladb.com>
The to_metrics_summary is a helper function that create a metrics type
summary from a timed_rate_moving_average_with_summary object.
Signed-off-by: Amnon Heiman <amnon@scylladb.com>
Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
This patch aim to make the implementation and usage of the
approx_exponential_histogram clearer.
The approx_exponential_histogram Uses a combination of Min, Max,
Precision and number of buckets where the user needs to pick 3.
Most of the changes in the patch are about documenting the class and
method, but following the review there are two functionality changes:
1. The user would pick: Min, Max and Precision and the number of buckets
will be calculated from these values.
2. The template restrictions are now state in a requires so voiolation
will be stop at compile time.
This patch adds a helper converter function to convert from a
approx_exponential_histogram histogram to a seastar::metrics::histogram
Signed-off-by: Amnon Heiman <amnon@scylladb.com>
