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Clarify ordering more

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Instead of saying what users should not do, provide a positive
recommendation.

Signed-off-by: Matthias Rampke <matthias@prometheus.io>
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Matthias Rampke 2021-01-22 12:55:37 +00:00
parent 64c79eea8b
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README.md
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@ -240,15 +240,21 @@ mappings:
``` ```
Glob matching offers the best performance for common mappings. Glob matching offers the best performance for common mappings.
There are however pathological cases like the following matches:
a.*.*.*.* #### Ordering glob rules
a.b.*.*.*
a.b.c.*.*
a.b.c.d.*
Optimize these mappings by reversing the order, or by disabling mapping ordering. List more specific matches before wildcards, from left to right:
a.b.c
a.b.*
a.*.d
a.*.*
This avoids unexpected shadowing of later rules, and performance impact from backtracking.
Alternatively, you can disable mapping ordering altogether.
With unordered mapping, at each hierarchy level the most specific match wins. With unordered mapping, at each hierarchy level the most specific match wins.
This has the same effect as using the recommended ordering.
### Regular expression matching ### Regular expression matching
@ -258,6 +264,7 @@ Use it if the glob mapping is not flexible enough to pull structured data from t
Regular expression matching is significantly slower than glob mapping as all mappings must be tested in order. Regular expression matching is significantly slower than glob mapping as all mappings must be tested in order.
Because of this, **regex mappings are only executed after all glob mappings**. Because of this, **regex mappings are only executed after all glob mappings**.
In other words, glob mappings take preference over regex matches, irrespective of the order in which they are specified. In other words, glob mappings take preference over regex matches, irrespective of the order in which they are specified.
Regular expression matches are always evaluated in order, and the first match wins.
The metric name can also contain references to regex matches. The mapping above The metric name can also contain references to regex matches. The mapping above
could be written as: could be written as:
@ -289,6 +296,7 @@ mappings:
labels: labels:
provider: "$1" provider: "$1"
``` ```
### Naming, labels, and help ### Naming, labels, and help
Please note that metrics with the same name must also have the same set of Please note that metrics with the same name must also have the same set of