[3.2] Add information about log levels [docs]

docs/01_nodeos/06_logging/01_logging-levels.md

@@ -64,3 +64,24 @@ Sample `logging.json`:
  ]
 }
 ```
+
+## Expected Output of Log Levels
+
+* `error` - Log output that likely requires operator intervention.
+  - Error level logging should be reserved for conditions that are completely unexpected or otherwise need human intervention.
+  - Also used to indicate software errors such as: impossible values for an `enum`, out of bounds array access, null pointers, or other conditions that likely will throw an exception.
+  - *Note*: Currently, there are numerous `error` level logging that likely should be `warn` as they do not require human intervention. The `net_plugin_impl`, for example, has a number of `error` level logs for bad network connections. This is handled and processed correctly. These should be changed to `warn` or `info`.
+* `warn` - Log output indicating unexpected but recoverable errors.
+  - Although, `warn` level typically does not require human intervention, repeated output of `warn` level logs might indicate actions needed by an operator.
+  - `warn` should not be used simply for conveying information. A `warn` level log is something to take notice of, but not necessarily be concerned about.
+* `info` (default) - Log output that provides useful information to an operator.
+  - Can be just progress indication or other useful data to a user. Care is taken not to create excessive log output with `info` level logging. For example, no `info` level logging should be produced for every transaction.
+  - For progress indication, some multiple of transactions should be processed between each log output; typically, every 1000 transactions.
+* `debug` - Useful log output for when non-default logging is enabled.
+  - Answers the question: is this useful information for a user that is monitoring the log output. Care should be taken not to create excessive log output; similar to `info` level logging.
+  - Enabling `debug` level logging should provide greater insight into behavior without overwhelming the output with log entries.
+  - `debug` level should not be used for *trace* level logging; to that end, use `all` (see below).
+  - Like `info`, no `debug` level logging should be produced for every transaction. There are specific transaction level loggers dedicated to transaction level logging: `transaction`, `transaction_trace_failure`, `transaction_trace_success`, `transaction_failure_tracing`, `transaction_success_tracing`.
+* `all` (trace) - For logging that would be overwhelming if `debug` level logging were used.
+  - Can be used for trace level logging. Only used in a few places and not completely supported.
+  - *Note*: In the future a different logging library may provide better trace level logging support. The current logging framework is not performant enough to enable excess trace level output.