# LoggerEtsBackend
[][1]
A simple `Logger` backend which writes log entries to an ETS table.
It does not create or manage the table for you; you must do this
external to the logging app.
`LoggerEtsBackend` borrows heavily from [`LoggerFileBackend`][2], and
therefore acts much the same way.
## Rationale
The primary use-case for this backend is _not_ for persistent logs,
but for temporary logs that may need to be inspected at run-time by
the system itself. By pushing log messages to an ETS table, data can
be quickly searched using `match_spec`s based on message contents or
the metadata stored along with the entry.
## Configuration
`LoggerEtsBackend` is a custom backend for the elixir `:logger`
application. This backend can only log to a single ETS table, so there
must be one `:logger` backend configured for each log file we
need. Each backend has a name like `{LoggerEtsBackend, id}`, where
`id` is any elixir term (usually an atom).
**Note:** tables use for logging are recommented to be configured with
the `:ordered_set` and `:public` options.
### Configuration Example
```elixir
config :logger,
backends: [{LoggerEtsBackend, :inspection_log}]
# configuration for the {LoggerEtsBackend, :critical_log} backend
config :logger, :critical_log,
table: :critical_table,
level: :error
```
## Usage
`LoggerEtsBackend` supports the following configuration values:
* `table` - the table name to push log tuples to
* `level` - the logging level for the backend
* `metadata` - the metadata to include
* `metadata_filter` - metadata terms which must be present in order to
log
**Note:** It is recommended that `metadata_filter` is set for this
backend, to ensure only a small subset of log entries are captured.
### Examples
#### Runtime configuration
```elixir
# some process starts an ets table
:ets.new(:debug_messages, [:ordered_set, :public, :named_table])
...
Logger.add_backend {LoggerFileBackend, :debug}
Logger.configure_backend {LoggerFileBackend, :debug},
table: :debug_messages,
metadata: ...,
metadata_filter: ...
```
#### Application config for multiple log files
```elixir
config :logger,
backends: [{LoggerEtsBackend, :info},
{LoggerEtsBackend, :error}]
config :logger, :info,
table: :info_messages,
level: :info
config :logger, :error,
table: :error_messages,
level: :error
```
#### Filter out metadata
This example removes all the default metadata and only keeps the
`:module` name which issued the log message.
```elixir
config :logger,
backends: [{LoggerEtsBackend, :info}]
config :logger, :info,
table: :info_messages,
level: :info,
metadata: [application: :ui]
```
#### Filtering logging by specifying metadata terms
This example only logs `:info` statements originating from the `:ui`
OTP app. The `:application` metadata key is auto-populated by
`Logger`.
```elixir
config :logger,
backends: [{LoggerEtsBackend, :ui}]
config :logger, :ui,
table: :ui_messages,
level: :info,
metadata_filter: [application: :ui]
```
[1]: https://travis-ci.org/OldhamMade/logger_ets_backend
[2]: https://github.com/onkel-dirtus/logger_file_backend
