Remove stacktrace from connection acquisition attempts in LoadBalancer (neo4j#944)

This is to reduce the noise in the logs on connection acquisition errors. Complete failures are reported separately.

Author: injectives

driver/src/main/java/org/neo4j/driver/internal/cluster/RediscoveryImpl.java

@@ -60,6 +60,9 @@ public class RediscoveryImpl implements Rediscovery
 {
     private static final String NO_ROUTERS_AVAILABLE = "Could not perform discovery for database '%s'. No routing server available.";
     private static final String RECOVERABLE_ROUTING_ERROR = "Failed to update routing table with server '%s'.";
+    private static final String RECOVERABLE_DISCOVERY_ERROR_WITH_SERVER = "Received a recoverable discovery error with server '%s', " +
+                                                                          "will continue discovery with other routing servers if available. " +
+                                                                          "Complete failure is reported separately from this entry.";
 
     private final BoltServerAddress initialRouter;
     private final RoutingSettings settings;
@@ -291,8 +294,9 @@ private ClusterComposition handleRoutingProcedureError( Throwable error, Routing
         // Retriable error happened during discovery.
         DiscoveryException discoveryError = new DiscoveryException( format( RECOVERABLE_ROUTING_ERROR, routerAddress ), error );
         Futures.combineErrors( baseError, discoveryError ); // we record each failure here
-        logger.warn( format( "Received a recoverable discovery error with server '%s', will continue discovery with other routing servers if available.",
-                routerAddress ), discoveryError );
+        String warningMessage = format( RECOVERABLE_DISCOVERY_ERROR_WITH_SERVER, routerAddress );
+        logger.warn( warningMessage );
+        logger.debug( warningMessage, discoveryError );
         routingTable.forget( routerAddress );
         return null;
     }

driver/src/main/java/org/neo4j/driver/internal/cluster/loadbalancing/LoadBalancer.java

@@ -20,6 +20,7 @@
 
 import io.netty.util.concurrent.EventExecutorGroup;
 
+import java.util.LinkedList;
 import java.util.List;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CompletionStage;
@@ -62,6 +63,11 @@
 public class LoadBalancer implements ConnectionProvider
 {
     private static final String LOAD_BALANCER_LOG_NAME = "LoadBalancer";
+    private static final String CONNECTION_ACQUISITION_COMPLETION_FAILURE_MESSAGE = "Connection acquisition failed for all available addresses.";
+    private static final String CONNECTION_ACQUISITION_COMPLETION_EXCEPTION_MESSAGE =
+            "Failed to obtain connection towards %s server. Known routing table is: %s";
+    private static final String CONNECTION_ACQUISITION_ATTEMPT_FAILURE_MESSAGE =
+            "Failed to obtain a connection towards address %s, will try other addresses if available. Complete failure is reported separately from this entry.";
     private final ConnectionPool connectionPool;
     private final RoutingTableRegistry routingTables;
     private final LoadBalancingStrategy loadBalancingStrategy;
@@ -181,19 +187,23 @@ private CompletionStage<Connection> acquire( AccessMode mode, RoutingTable routi
     {
         AddressSet addresses = addressSet( mode, routingTable );
         CompletableFuture<Connection> result = new CompletableFuture<>();
-        acquire( mode, routingTable, addresses, result );
+        List<Throwable> attemptExceptions = new LinkedList<>();
+        acquire( mode, routingTable, addresses, result, attemptExceptions );
         return result;
     }
 
-    private void acquire( AccessMode mode, RoutingTable routingTable, AddressSet addresses, CompletableFuture<Connection> result )
+    private void acquire( AccessMode mode, RoutingTable routingTable, AddressSet addresses, CompletableFuture<Connection> result,
+                          List<Throwable> attemptErrors )
     {
         BoltServerAddress address = selectAddress( mode, addresses );
 
         if ( address == null )
         {
-            result.completeExceptionally( new SessionExpiredException(
-                    "Failed to obtain connection towards " + mode + " server. " +
-                    "Known routing table is: " + routingTable ) );
+            SessionExpiredException completionError =
+                    new SessionExpiredException( format( CONNECTION_ACQUISITION_COMPLETION_EXCEPTION_MESSAGE, mode, routingTable ) );
+            attemptErrors.forEach( completionError::addSuppressed );
+            log.error( CONNECTION_ACQUISITION_COMPLETION_FAILURE_MESSAGE, completionError );
+            result.completeExceptionally( completionError );
             return;
         }
 
@@ -204,10 +214,12 @@ private void acquire( AccessMode mode, RoutingTable routingTable, AddressSet add
             {
                 if ( error instanceof ServiceUnavailableException )
                 {
-                    SessionExpiredException errorToLog = new SessionExpiredException( format( "Server at %s is no longer available", address ), error );
-                    log.warn( "Failed to obtain a connection towards address " + address, errorToLog );
+                    String attemptMessage = format( CONNECTION_ACQUISITION_ATTEMPT_FAILURE_MESSAGE, address );
+                    log.warn( attemptMessage );
+                    log.debug( attemptMessage, error );
+                    attemptErrors.add( error );
                     routingTable.forget( address );
-                    eventExecutorGroup.next().execute( () -> acquire( mode, routingTable, addresses, result ) );
+                    eventExecutorGroup.next().execute( () -> acquire( mode, routingTable, addresses, result, attemptErrors ) );
                 }
                 else
                 {