Reduce sharding warnings when there are no buffered messages (#29525)

* Reduce sharding warnings when there are no buffered messages

If shard regions are started before the cluster is formed warnings are
logged. The user can wait until SelfUp but for the cases they don't make
logging debug until the user has buffered messages.

* Review feedback

* Review feedback

akka-cluster-sharding/src/main/scala/akka/cluster/sharding/ShardRegion.scala

@@ -931,12 +931,23 @@ private[akka] class ShardRegion(
         val coordinatorMessage =
           if (cluster.state.unreachable(membersByAge.head)) s"Coordinator [${membersByAge.head}] is unreachable."
           else s"Coordinator [${membersByAge.head}] is reachable."
-        log.warning(
-          "{}: Trying to register to coordinator at [{}], but no acknowledgement. Total [{}] buffered messages. [{}]",
-          typeName,
-          actorSelections.mkString(", "),
-          shardBuffers.totalSize,
-          coordinatorMessage)
+        val bufferSize = shardBuffers.totalSize
+        if (bufferSize > 0) {
+          if (log.isWarningEnabled) {
+            log.warning(
+              "{}: Trying to register to coordinator at [{}], but no acknowledgement. Total [{}] buffered messages. [{}]",
+              typeName,
+              actorSelections.mkString(", "),
+              bufferSize,
+              coordinatorMessage)
+          }
+        } else if (log.isDebugEnabled) {
+          log.debug(
+            "{}: Trying to register to coordinator at [{}], but no acknowledgement. No buffered messages yet. [{}]",
+            typeName,
+            actorSelections.mkString(", "),
+            coordinatorMessage)
+        }
       } else {
         // Members start off as "Removed"
         val partOfCluster = cluster.selfMember.status != MemberStatus.Removed
@@ -946,11 +957,17 @@ private[akka] class ShardRegion(
           else
             "Probably, no seed-nodes configured and manual cluster or bootstrap join not performed?"
 
-        log.warning(
-          "{}: No coordinator found to register. {} Total [{}] buffered messages.",
-          typeName,
-          possibleReason,
-          shardBuffers.totalSize)
+        val bufferSize = shardBuffers.totalSize
+        if (bufferSize > 0) {
+          log.warning(
+            "{}: No coordinator found to register. {} Total [{}] buffered messages.",
+            typeName,
+            possibleReason,
+            bufferSize)
+        } else {
+          log.debug("{}: No coordinator found to register. {} No buffered messages yet.", typeName, possibleReason)
+        }
+
       }
     }
   }