Change verbosity of state machine logs to trace

NEXT_CHANGELOG.md

@@ -172,6 +172,12 @@ Move the location of the `text` field when exposing the query plan and fill it w
 
 By [@bnjjj](https://github.com/bnjjj) in https://github.com/apollographql/router/pull/1557
 
+### Change state machine log messages to `trace` ([#1578](https://github.com/apollographql/router/issues/1578))
+
+We no longer show internal state machine log events at the `info` level since they are unnecessary during normal operation.  They are instead emitted at the `trace` level and can be enabled selectively using the `--log trace` flag.
+
+By [@abernix](https://github.com/abernix) in https://github.com/apollographql/router/pull/1597
+
 ### Formatting problem fix of scalar fields selected several times ([PR #1583](https://github.com/apollographql/router/issues/1583))
 
 Fixed a bug where querying scalar fields several times would put `null`s instead of expected values.

apollo-router/src/state_machine.rs

@@ -227,7 +227,7 @@ where
                 }
             };
 
-            tracing::info!("transitioned to {}", &new_state);
+            tracing::trace!("transitioned to {}", &new_state);
             state = new_state;
 
             // If we're running then let those waiting proceed.