# Exporter Helper

This is a helper exporter that other exporters can depend on. Today, it primarily offers queued retry capabilities.

> :warning: This exporter should not be added to a service pipeline.

## Configuration

The following configuration options can be modified:

- `retry_on_failure`
  - `enabled` (default = true)
  - `initial_interval` (default = 5s): Time to wait after the first failure before retrying; ignored if `enabled` is `false`
  - `max_interval` (default = 30s): Is the upper bound on backoff; ignored if `enabled` is `false`
  - `max_elapsed_time` (default = 300s): Is the maximum amount of time spent trying to send a batch; ignored if `enabled` is `false`. If set to 0, the retries are never stopped.
- `sending_queue`
  - `enabled` (default = true)
  - `num_consumers` (default = 10): Number of consumers that dequeue batches; ignored if `enabled` is `false`
  - `blocking` (default = false): If true, blocks the request until the queue has space otherwise returns immediately; ignored if `enabled` is `false`
  - `queue_size` (default = 1000): Maximum number of batches kept in memory before dropping; ignored if `enabled` is `false`. User should calculate this as `num_seconds * requests_per_second / requests_per_batch` where:
    - `num_seconds` is the number of seconds to buffer in case of a backend outage
    - `requests_per_second` is the average number of requests per seconds
    - `requests_per_batch` is the average number of requests per batch (if 
      [the batch processor](https://github.com/open-telemetry/opentelemetry-collector/tree/main/processor/batchprocessor)
      is used, the metric `send_batch_size` can be used for estimation)
- `timeout` (default = 5s): Time to wait per individual attempt to send data to a backend

The `initial_interval`, `max_interval`, `max_elapsed_time`, and `timeout` options accept 
[duration strings](https://pkg.go.dev/time#ParseDuration),
valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h".

### Persistent Queue

To use the persistent queue, the following setting needs to be set:

- `sending_queue`
  - `storage` (default = none): When set, enables persistence and uses the component specified as a storage extension for the persistent queue.
    There is no in-memory queue when set.

The maximum number of batches stored to disk can be controlled using `sending_queue.queue_size` parameter (which,
similarly as for in-memory buffering, defaults to 1000 batches).

When persistent queue is enabled, the batches are being buffered using the provided storage extension - [filestorage] is a popular and safe choice. If the collector instance is killed while having some items in the persistent queue, on restart the items will be picked and the exporting is continued.

```
                                                              ┌─Consumer #1─┐
                                                              │    ┌───┐    │
                              ──────Deleted──────        ┌───►│    │ 1 │    ├───► Success
        Waiting in channel    x           x     x        │    │    └───┘    │
        for consumer ───┐     x           x     x        │    │             │
                        │     x           x     x        │    └─────────────┘
                        ▼     x           x     x        │
┌─────────────────────────────────────────x─────x───┐    │    ┌─Consumer #2─┐
│                             x           x     x   │    │    │    ┌───┐    │
│     ┌───┐     ┌───┐ ┌───┐ ┌─x─┐ ┌───┐ ┌─x─┐ ┌─x─┐ │    │    │    │ 2 │    ├───► Permanent -> X
│ n+1 │ n │ ... │ 6 │ │ 5 │ │ 4 │ │ 3 │ │ 2 │ │ 1 │ ├────┼───►│    └───┘    │      failure
│     └───┘     └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ │    │    │             │
│                                                   │    │    └─────────────┘
└───────────────────────────────────────────────────┘    │
   ▲              ▲     ▲           ▲                    │    ┌─Consumer #3─┐
   │              │     │           │                    │    │    ┌───┐    │
   │              │     │           │                    │    │    │ 3 │    ├───► (in progress)
 write          read    └─────┬─────┘                    ├───►│    └───┘    │
 index          index         │                          │    │             │
                              │                          │    └─────────────┘
                              │                          │
                          currently                      │    ┌─Consumer #4─┐
                          dispatched                     │    │    ┌───┐    │     Temporary
                                                         └───►│    │ 4 │    ├───►  failure
                                                              │    └───┘    │         │
                                                              │             │         │
                                                              └─────────────┘         │
                                                                     ▲                │
                                                                     └── Retry ───────┤
                                                                                      │
                                                                                      │
                                                   X  ◄────── Retry limit exceeded ───┘
```

Example:

```
receivers:
  otlp:
    protocols:
      grpc:
exporters:
  otlp:
    endpoint: <ENDPOINT>
    sending_queue:
      storage: file_storage/otc
extensions:
  file_storage/otc:
    directory: /var/lib/storage/otc
    timeout: 10s
service:
  extensions: [file_storage]
  pipelines:
    metrics:
      receivers: [otlp]
      exporters: [otlp]
    logs:
      receivers: [otlp]
      exporters: [otlp]
    traces:
      receivers: [otlp]
      exporters: [otlp]

```

[filestorage]: https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/extension/storage/filestorage
