mirror of
https://github.com/open-telemetry/opentelemetry-go.git
synced 2024-12-14 10:13:10 +02:00
137 lines
6.6 KiB
Go
137 lines
6.6 KiB
Go
// Copyright The OpenTelemetry Authors
|
|
//
|
|
// Licensed under the Apache License, Version 2.0 (the "License");
|
|
// you may not use this file except in compliance with the License.
|
|
// You may obtain a copy of the License at
|
|
//
|
|
// http://www.apache.org/licenses/LICENSE-2.0
|
|
//
|
|
// Unless required by applicable law or agreed to in writing, software
|
|
// distributed under the License is distributed on an "AS IS" BASIS,
|
|
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
// See the License for the specific language governing permissions and
|
|
// limitations under the License.
|
|
|
|
/*
|
|
Package metric implements the OpenTelemetry metric.MeterImpl
|
|
interface. The Accumulator type supports configurable metrics export
|
|
behavior through a collection of export interfaces that support
|
|
various export strategies, described below.
|
|
|
|
The metric.MeterImpl API consists of methods for constructing
|
|
synchronous and asynchronous instruments. There are two constructors
|
|
per instrument for the two kinds of number (int64, float64).
|
|
|
|
Synchronous instruments are managed by a sync.Map containing a *record
|
|
with the current state for each synchronous instrument. A bound
|
|
instrument encapsulates a direct pointer to the record, allowing
|
|
bound metric events to bypass a sync.Map lookup. A lock-free
|
|
algorithm is used to protect against races when adding and removing
|
|
items from the sync.Map.
|
|
|
|
Asynchronous instruments are managed by an internal
|
|
AsyncInstrumentState, which coordinates calling batch and single
|
|
instrument callbacks.
|
|
|
|
Internal Structure
|
|
|
|
Each observer also has its own kind of record stored in the SDK. This
|
|
record contains a set of recorders for every specific label set used in the
|
|
callback.
|
|
|
|
A sync.Map maintains the mapping of current instruments and label sets to
|
|
internal records. To create a new bound instrument, the SDK consults the Map to
|
|
locate an existing record, otherwise it constructs a new record. The SDK
|
|
maintains a count of the number of references to each record, ensuring
|
|
that records are not reclaimed from the Map while they are still active
|
|
from the user's perspective.
|
|
|
|
Metric collection is performed via a single-threaded call to Collect that
|
|
sweeps through all records in the SDK, checkpointing their state. When a
|
|
record is discovered that has no references and has not been updated since
|
|
the prior collection pass, it is removed from the Map.
|
|
|
|
Both synchronous and asynchronous instruments have an associated
|
|
aggregator, which maintains the current state resulting from all metric
|
|
events since its last checkpoint. Aggregators may be lock-free or they may
|
|
use locking, but they should expect to be called concurrently. Aggregators
|
|
must be capable of merging with another aggregator of the same type.
|
|
|
|
Export Pipeline
|
|
|
|
While the SDK serves to maintain a current set of records and
|
|
coordinate collection, the behavior of a metrics export pipeline is
|
|
configured through the export types in
|
|
go.opentelemetry.io/otel/sdk/export/metric. It is important to keep
|
|
in mind the context these interfaces are called from. There are two
|
|
contexts, instrumentation context, where a user-level goroutine that
|
|
enters the SDK resulting in a new record, and collection context,
|
|
where a system-level thread performs a collection pass through the
|
|
SDK.
|
|
|
|
Descriptor is a struct that describes the metric instrument to the
|
|
export pipeline, containing the name, units, description, metric kind,
|
|
number kind (int64 or float64). A Descriptor accompanies metric data
|
|
as it passes through the export pipeline.
|
|
|
|
The AggregatorSelector interface supports choosing the method of
|
|
aggregation to apply to a particular instrument, by delegating the
|
|
construction of an Aggregator to this interface. Given the Descriptor,
|
|
the AggregatorFor method returns an implementation of Aggregator. If this
|
|
interface returns nil, the metric will be disabled. The aggregator should
|
|
be matched to the capabilities of the exporter. Selecting the aggregator
|
|
for Adding instruments is relatively straightforward, but many options
|
|
are available for aggregating distributions from Grouping instruments.
|
|
|
|
Aggregator is an interface which implements a concrete strategy for
|
|
aggregating metric updates. Several Aggregator implementations are
|
|
provided by the SDK. Aggregators may be lock-free or use locking,
|
|
depending on their structure and semantics. Aggregators implement an
|
|
Update method, called in instrumentation context, to receive a single
|
|
metric event. Aggregators implement a Checkpoint method, called in
|
|
collection context, to save a checkpoint of the current state.
|
|
Aggregators implement a Merge method, also called in collection
|
|
context, that combines state from two aggregators into one. Each SDK
|
|
record has an associated aggregator.
|
|
|
|
Processor is an interface which sits between the SDK and an exporter.
|
|
The Processor embeds an AggregatorSelector, used by the SDK to assign
|
|
new Aggregators. The Processor supports a Process() API for submitting
|
|
checkpointed aggregators to the processor, and a CheckpointSet() API
|
|
for producing a complete checkpoint for the exporter. Two default
|
|
Processor implementations are provided, the "defaultkeys" Processor groups
|
|
aggregate metrics by their recommended Descriptor.Keys(), the
|
|
"simple" Processor aggregates metrics at full dimensionality.
|
|
|
|
LabelEncoder is an optional optimization that allows an exporter to
|
|
provide the serialization logic for labels. This allows avoiding
|
|
duplicate serialization of labels, once as a unique key in the SDK (or
|
|
Processor) and once in the exporter.
|
|
|
|
CheckpointSet is an interface between the Processor and the Exporter.
|
|
After completing a collection pass, the Processor.CheckpointSet() method
|
|
returns a CheckpointSet, which the Exporter uses to iterate over all
|
|
the updated metrics.
|
|
|
|
Record is a struct containing the state of an individual exported
|
|
metric. This is the result of one collection interface for one
|
|
instrument and one label set.
|
|
|
|
Labels is a struct containing an ordered set of labels, the
|
|
corresponding unique encoding, and the encoder that produced it.
|
|
|
|
Exporter is the final stage of an export pipeline. It is called with
|
|
a CheckpointSet capable of enumerating all the updated metrics.
|
|
|
|
Controller is not an export interface per se, but it orchestrates the
|
|
export pipeline. For example, a "push" controller will establish a
|
|
periodic timer to regularly collect and export metrics. A "pull"
|
|
controller will await a pull request before initiating metric
|
|
collection. Either way, the job of the controller is to call the SDK
|
|
Collect() method, then read the checkpoint, then invoke the exporter.
|
|
Controllers are expected to implement the public metric.MeterProvider
|
|
API, meaning they can be installed as the global Meter provider.
|
|
|
|
*/
|
|
package metric // import "go.opentelemetry.io/otel/sdk/metric"
|