[3.2] Add information about log levels [docs]

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

@@ -64,3 +64,43 @@ 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 needs human
+    intervention. 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 may indicate action is needed by an operator. `warn` should not be used
+    for simply 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 just be 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 to not create excessive log output; similar to `info` level
+    logging. `debug` level should not be used for `trace` level logging. Enabling
+    `debug` level logging should provide greater insight into behavior without
+    overwhelming the output with log entries. 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)
+  * `all` level logging is for logging that would be overwhelming if it was `debug`
+    level logging. Only used in a few places and not completely supported. 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.