diff --git a/source/net/yacy/cora/federate/solr/connector/ConcurrentUpdateSolrConnector.java b/source/net/yacy/cora/federate/solr/connector/ConcurrentUpdateSolrConnector.java
index 7c7428e00..792d921ad 100644
--- a/source/net/yacy/cora/federate/solr/connector/ConcurrentUpdateSolrConnector.java
+++ b/source/net/yacy/cora/federate/solr/connector/ConcurrentUpdateSolrConnector.java
@@ -329,6 +329,7 @@ public class ConcurrentUpdateSolrConnector implements SolrConnector {
     public Set<String> existsByIds(Set<String> ids) throws IOException {
         HashSet<String> e = new HashSet<String>();
         if (ids == null || ids.size() == 0) return e;
+        if (ids.size() == 1) return existsById(ids.iterator().next()) ? ids : e;
         Set<String> idsC = new HashSet<String>();
         for (String id: ids) {
             if (this.idCache.has(ASCII.getBytes(id))) {cacheSuccessSign(); e.add(id); continue;}
diff --git a/source/net/yacy/cora/federate/solr/connector/MirrorSolrConnector.java b/source/net/yacy/cora/federate/solr/connector/MirrorSolrConnector.java
index 282ab65d0..c6d51e8ec 100644
--- a/source/net/yacy/cora/federate/solr/connector/MirrorSolrConnector.java
+++ b/source/net/yacy/cora/federate/solr/connector/MirrorSolrConnector.java
@@ -348,6 +348,8 @@ public class MirrorSolrConnector extends AbstractSolrConnector implements SolrCo
 
     @Override
     public Set<String> existsByIds(Set<String> ids) throws IOException {
+        if (ids == null || ids.size() == 0) return new HashSet<String>();
+        if (ids.size() == 1) return existsById(ids.iterator().next()) ? ids : new HashSet<String>();
         if (this.solr0 != null && this.solr1 == null) return this.solr0.existsByIds(ids);
         if (this.solr0 == null && this.solr1 != null) return this.solr1.existsByIds(ids);
         Set<String> s = new HashSet<String>();
diff --git a/source/net/yacy/peers/Transmission.java b/source/net/yacy/peers/Transmission.java
index 47799fd7c..44fd4a807 100644
--- a/source/net/yacy/peers/Transmission.java
+++ b/source/net/yacy/peers/Transmission.java
@@ -25,7 +25,6 @@
 package net.yacy.peers;
 
 import java.util.ArrayList;
-import java.util.Collection;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
@@ -164,7 +163,7 @@ public class Transmission {
             final ReferenceContainer<WordReference> c = (remaining >= container.size()) ? container : trimContainer(container, remaining);
             // iterate through the entries in the container and check if the reference is in the repository
             final List<byte[]> notFoundx = new ArrayList<byte[]>();
-            Collection<String> testids = new HashSet<String>();
+            Set<String> testids = new HashSet<String>();
             Iterator<WordReference>  i = c.entries();
             while (i.hasNext()) {
                 final WordReference e = i.next();
diff --git a/source/net/yacy/search/Switchboard.java b/source/net/yacy/search/Switchboard.java
index e392cab37..c828ac3ad 100644
--- a/source/net/yacy/search/Switchboard.java
+++ b/source/net/yacy/search/Switchboard.java
@@ -1585,7 +1585,7 @@ public final class Switchboard extends serverSwitch {
      * @param ids a collection of url hashes
      * @return a map from the hash id to: if it exists, the name of the database, otherwise null
      */
-    public Map<String, HarvestProcess> urlExists(final Collection<String> ids) {
+    public Map<String, HarvestProcess> urlExists(final Set<String> ids) {
         Set<String> e = this.index.exists(ids);
         Map<String, HarvestProcess> m = new HashMap<String, HarvestProcess>();
         for (String id: ids) {
@@ -2905,7 +2905,7 @@ public final class Switchboard extends serverSwitch {
         // stacking may fail because of double occurrences of that url. Therefore
         // we must wait here until the url has actually disappeared
         int t = 100;
-        Collection<String> ids = new ArrayList<String>(1); ids.add(ASCII.String(urlhash));
+        Set<String> ids = new HashSet<String>(1); ids.add(ASCII.String(urlhash));
         while (t-- > 0 && this.index.exists(ids).size() > 0) {
             try {Thread.sleep(100);} catch (final InterruptedException e) {}
             ConcurrentLog.fine("Switchboard", "STACKURL: waiting for deletion, t=" + t);
diff --git a/source/net/yacy/search/index/Fulltext.java b/source/net/yacy/search/index/Fulltext.java
index 58f3e3a8f..39ed4d89a 100644
--- a/source/net/yacy/search/index/Fulltext.java
+++ b/source/net/yacy/search/index/Fulltext.java
@@ -617,9 +617,10 @@ public final class Fulltext {
      * @param ids
      * @return a set of ids which exist in the database
      */
-    public Set<String> exists(Collection<String> ids) {
+    public Set<String> exists(Set<String> ids) {
         HashSet<String> e = new HashSet<String>();
         if (ids == null || ids.size() == 0) return e;
+        if (ids.size() == 1) return exists(ids.iterator().next()) ? ids : e;
         Set<String> idsC = new HashSet<String>();
         idsC.addAll(ids);
         if (this.urlIndexFile != null) {
diff --git a/source/net/yacy/search/index/Segment.java b/source/net/yacy/search/index/Segment.java
index 918458837..df479736b 100644
--- a/source/net/yacy/search/index/Segment.java
+++ b/source/net/yacy/search/index/Segment.java
@@ -29,7 +29,6 @@ package net.yacy.search.index;
 import java.io.File;
 import java.io.IOException;
 import java.net.MalformedURLException;
-import java.util.Collection;
 import java.util.Date;
 import java.util.Iterator;
 import java.util.List;
@@ -443,7 +442,7 @@ public class Segment {
      * @param ids
      * @return a set of ids which exist in the database
      */
-    public Set<String> exists(final Collection<String> ids) {
+    public Set<String> exists(final Set<String> ids) {
         return this.fulltext.exists(ids);
     }