| Overview |  |
The main idea behind this filter that the processing of the spans can be modified runtime by changing the filter configuration. This way logging, counting or sending data to trace collectors can be modified on the running system based on the changing operational requirements.
The span filter works with key value pair lists. This was the easiest to implement and reasonably fast.
Filter rules are composed by a list of {Conditions, Actions} tuples.
Processing a span means iterating through this list and when an item
found where all Conditions evaluate to true then the Actions in that
item are executed.
Conditions operate on a copy of the tags of the span. It is a
sequence of checks against the tags (e.g. key present, key value)
where if any check in the sequence fails, the associated actions are
not executed and the next {Conditions, Actions} item is evaluated.
Actions can trigger e.g. counting a particular tag value combination,
logging, sending the span to trace collectors, modifying the working
(i.e. used for further conditions) tag list, modifying the span tag
list that is to be sent to trace collector. Actions can also
influence the further evaluation of the rules i.e. providing the
break action instructs the rule engine NOT to look further in the
list of {Conditions, Actions}.
Evaluation of the rules happens in the process which invokes the span
end statement (e.g. @link otter:finish/1.) i.e. it has impact on the
request processing time. Therefore the actions that consume little
time and resources with no external interfaces (e.g. counting in ets)
can be done during the evaluation of the rules, but anything that has
external interface or dependent on environment (e.g. logging and trace
collecting) should be done asynchronously.
| span/1 | Takes a span as input, evaluates rules specified in configuration and executes any specified actions. |
span(Span::span()) -> ok
Takes a span as input, evaluates rules specified in configuration and executes any specified actions.
Generated by EDoc, Apr 14 2017, 04:39:45.