diff --git a/source/net/yacy/cora/federate/solr/connector/ConcurrentUpdateSolrConnector.java b/source/net/yacy/cora/federate/solr/connector/ConcurrentUpdateSolrConnector.java
index 9eb75070f..5d8c80dad 100644
--- a/source/net/yacy/cora/federate/solr/connector/ConcurrentUpdateSolrConnector.java
+++ b/source/net/yacy/cora/federate/solr/connector/ConcurrentUpdateSolrConnector.java
@@ -126,6 +126,16 @@ public class ConcurrentUpdateSolrConnector implements SolrConnector {
         ensureAliveProcessHandler();
     }
 
+    @Override
+    public int hashCode() {
+        return this.connector.hashCode();
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        return o instanceof ConcurrentUpdateSolrConnector && this.connector.equals(((ConcurrentUpdateSolrConnector) o).connector);
+    }
+
     @Override
     public int bufferSize() {
         return this.processQueue.size();
diff --git a/source/net/yacy/cora/federate/solr/connector/EmbeddedSolrConnector.java b/source/net/yacy/cora/federate/solr/connector/EmbeddedSolrConnector.java
index 366990b09..8c035d5b6 100644
--- a/source/net/yacy/cora/federate/solr/connector/EmbeddedSolrConnector.java
+++ b/source/net/yacy/cora/federate/solr/connector/EmbeddedSolrConnector.java
@@ -98,6 +98,16 @@ public class EmbeddedSolrConnector extends SolrServerConnector implements SolrCo
         this.requestHandler.inform(this.core);
         super.init(this.instance.getServer(coreName));
     }
+
+    @Override
+    public int hashCode() {
+        return this.instance.hashCode();
+    }
+    
+    @Override
+    public boolean equals(Object o) {
+        return o instanceof EmbeddedSolrConnector && this.instance.equals(((EmbeddedSolrConnector) o).instance);
+    }
     
     @Override
     public int bufferSize() {
diff --git a/source/net/yacy/cora/federate/solr/connector/MirrorSolrConnector.java b/source/net/yacy/cora/federate/solr/connector/MirrorSolrConnector.java
index 8e4b46fd6..fa38beae7 100644
--- a/source/net/yacy/cora/federate/solr/connector/MirrorSolrConnector.java
+++ b/source/net/yacy/cora/federate/solr/connector/MirrorSolrConnector.java
@@ -52,6 +52,19 @@ public class MirrorSolrConnector extends AbstractSolrConnector implements SolrCo
         this.solr0 = solr0;
         this.solr1 = solr1;
     }
+
+    @Override
+    public int hashCode() {
+        return (this.solr0 == null ? 0 : this.solr0.hashCode()) + (this.solr1 == null ? 0 : this.solr1.hashCode());
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        return o instanceof MirrorSolrConnector &&
+                ((this.solr0 == null && ((MirrorSolrConnector) o).solr0 == null) || (((this.solr0 != null && ((MirrorSolrConnector) o).solr0 != null)) && this.solr0.equals(((MirrorSolrConnector) o).solr0))) &&
+                ((this.solr1 == null && ((MirrorSolrConnector) o).solr1 == null) || (((this.solr1 != null && ((MirrorSolrConnector) o).solr1 != null)) && this.solr1.equals(((MirrorSolrConnector) o).solr1)));
+    }
+    
     
     @Override
     public int bufferSize() {
diff --git a/source/net/yacy/cora/federate/solr/connector/RemoteSolrConnector.java b/source/net/yacy/cora/federate/solr/connector/RemoteSolrConnector.java
index e620cee9b..dcf8bc0e3 100644
--- a/source/net/yacy/cora/federate/solr/connector/RemoteSolrConnector.java
+++ b/source/net/yacy/cora/federate/solr/connector/RemoteSolrConnector.java
@@ -66,6 +66,16 @@ public class RemoteSolrConnector extends SolrServerConnector implements SolrConn
         super.init(s);
     }
 
+    @Override
+    public int hashCode() {
+        return this.instance.hashCode();
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        return o instanceof RemoteSolrConnector && ((RemoteSolrConnector) o).instance.equals(this.instance);
+    }
+
     public SolrInstance getInstance() {
         return this.instance;
     }
diff --git a/source/net/yacy/cora/federate/solr/instance/EmbeddedInstance.java b/source/net/yacy/cora/federate/solr/instance/EmbeddedInstance.java
index c9eb0b1e6..7c79fd9b4 100644
--- a/source/net/yacy/cora/federate/solr/instance/EmbeddedInstance.java
+++ b/source/net/yacy/cora/federate/solr/instance/EmbeddedInstance.java
@@ -100,6 +100,16 @@ public class EmbeddedInstance implements SolrInstance {
         this.server.put(this.defaultCoreName, this.defaultCoreServer);
     }
 
+    @Override
+    public int hashCode() {
+        return this.containerPath.hashCode();
+    }
+    
+    @Override
+    public boolean equals(Object o) {
+        return o instanceof EmbeddedInstance && this.containerPath.equals(((EmbeddedInstance) o).containerPath);
+    }
+    
     private void initializeCoreConf(final File solr_config, final File containerPath, String coreName) {
 
         // ensure that default core path exists
diff --git a/source/net/yacy/cora/federate/solr/instance/InstanceMirror.java b/source/net/yacy/cora/federate/solr/instance/InstanceMirror.java
index e2c974d26..23f98f9ff 100644
--- a/source/net/yacy/cora/federate/solr/instance/InstanceMirror.java
+++ b/source/net/yacy/cora/federate/solr/instance/InstanceMirror.java
@@ -22,7 +22,9 @@ package net.yacy.cora.federate.solr.instance;
 
 import java.io.IOException;
 import java.util.Collection;
+import java.util.HashSet;
 import java.util.Map;
+import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 
 import net.yacy.cora.federate.solr.connector.ConcurrentUpdateSolrConnector;
@@ -92,7 +94,9 @@ public class InstanceMirror {
     }
 
     public synchronized void close() {
-        for (SolrConnector connector: this.mirrorConnectorCache.values()) connector.close();
+        Set<SolrConnector> connectors = new HashSet<SolrConnector>();
+        connectors.addAll(this.mirrorConnectorCache.values());
+        for (SolrConnector connector: connectors) connector.close();
         this.mirrorConnectorCache.clear();
     }
 
diff --git a/source/net/yacy/cora/federate/solr/instance/RemoteInstance.java b/source/net/yacy/cora/federate/solr/instance/RemoteInstance.java
index 9ca938a6e..10e73568c 100644
--- a/source/net/yacy/cora/federate/solr/instance/RemoteInstance.java
+++ b/source/net/yacy/cora/federate/solr/instance/RemoteInstance.java
@@ -183,6 +183,16 @@ public class RemoteInstance implements SolrInstance {
         if (this.defaultServer == null) throw new IOException("cannot connect to url " + url + " and connect core " + defaultCoreName);
     }
 
+    @Override
+    public int hashCode() {
+        return this.solrurl.hashCode();
+    }
+    
+    @Override
+    public boolean equals(Object o) {
+        return o instanceof RemoteInstance && ((RemoteInstance) o).solrurl.equals(this.solrurl);
+    }
+
     public String getAdminInterface() {
         final InetAddress localhostExternAddress = Domains.myPublicLocalIP();
         final String localhostExtern = localhostExternAddress == null ? "127.0.0.1" : localhostExternAddress.getHostAddress();