diff --git a/data-store/src/main/java/org/lucares/pdb/datastore/lang/QueryCompletionPdbLangParser.java b/data-store/src/main/java/org/lucares/pdb/datastore/lang/QueryCompletionPdbLangParser.java
index cae815e..04c5e47 100644
--- a/data-store/src/main/java/org/lucares/pdb/datastore/lang/QueryCompletionPdbLangParser.java
+++ b/data-store/src/main/java/org/lucares/pdb/datastore/lang/QueryCompletionPdbLangParser.java
@@ -1,6 +1,7 @@
 package org.lucares.pdb.datastore.lang;
 
 import java.util.BitSet;
+import java.util.Collections;
 import java.util.List;
 import java.util.SortedSet;
 import java.util.TreeSet;
@@ -19,14 +20,18 @@ import org.antlr.v4.runtime.tree.TerminalNode;
 import org.lucares.pdb.datastore.Proposal;
 import org.lucares.pdb.datastore.internal.DataStore;
 import org.lucares.utils.CollectionUtils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 public class QueryCompletionPdbLangParser extends PdbLangParser {
 
+	private static final Logger LOGGER = LoggerFactory.getLogger(QueryCompletionPdbLangParser.class);
+	
 	public class Listener implements PdbLangListener, ANTLRErrorListener {
 
 		private final int caretPosition;
 		private final DataStore dataStore;
-		private final SortedSet<Proposal> proposals = new TreeSet<>();
+		private final SortedSet<Proposal> proposals = Collections.synchronizedSortedSet(new TreeSet<>());
 		private final String query;
 
 		public Listener(final String query, final DataStore dataStore, final int caretPosition) {
@@ -51,6 +56,7 @@ public class QueryCompletionPdbLangParser extends PdbLangParser {
 					final SortedSet<String> proposedValues = getPropertyValuesByPrefix(propertyKey,
 							propertyValuePrefix);
 
+					final long startTime = System.nanoTime();
 					proposedValues.stream()//
 							.map(v -> {
 								final StringBuilder newQuery = new StringBuilder(query);
@@ -63,13 +69,17 @@ public class QueryCompletionPdbLangParser extends PdbLangParser {
 								return new Proposal(p, count> 0);
 							}).forEach(proposals::add);
 
+					LOGGER.trace("proposals for property value {} took {} ms", propertyValuePrefix, (System.nanoTime() - startTime) / 1_000_000.0);
 				} else if (_ctx instanceof IdentifierExpressionContext) {
+					final long startTime = System.nanoTime();
 					final String propertyKeyPrefix = node.getText().substring(0, caretPosition - start);
 
 					final StringBuilder newQueryPattern = new StringBuilder(query);
 					newQueryPattern.replace(start, end + 1, "%s");
 
 					addProposalsForKeys(propertyKeyPrefix, newQueryPattern.toString());
+					
+					LOGGER.trace("proposals for property key {} took {} ms", propertyKeyPrefix, (System.nanoTime() - startTime) / 1_000_000.0);
 				}
 			}
 		}