diff --git a/data-store/src/main/java/org/lucares/pdb/datastore/internal/DataStore.java b/data-store/src/main/java/org/lucares/pdb/datastore/internal/DataStore.java
index 6e257af..f3f6ecf 100644
--- a/data-store/src/main/java/org/lucares/pdb/datastore/internal/DataStore.java
+++ b/data-store/src/main/java/org/lucares/pdb/datastore/internal/DataStore.java
@@ -40,6 +40,8 @@ public class DataStore implements AutoCloseable {
 																// area
 	private static final Logger EXECUTE_QUERY_LOGGER = LoggerFactory
 			.getLogger("org.lucares.metrics.dataStore.executeQuery");
+	private static final Logger MAP_DOCS_TO_DOCID = LoggerFactory
+			.getLogger("org.lucares.metrics.dataStore.mapDocsToDocID");
 	private static final Logger LOGGER = LoggerFactory.getLogger(DataStore.class);
 
 	public static final char LISTING_FILE_SEPARATOR = ',';
@@ -322,8 +324,8 @@ public class DataStore implements AutoCloseable {
 
 				result.add(doc);
 			}
-			System.out.println(
-					"mapDocIdsToDocs(" + docIdsList.size() + "): " + (System.nanoTime() - start) / 1_000_000.0 + "ms");
+			MAP_DOCS_TO_DOCID.debug("mapDocIdsToDocs({}): {}ms", docIdsList.size(),
+					(System.nanoTime() - start) / 1_000_000.0);
 		}
 		return result;
 	}
diff --git a/data-store/src/main/java/org/lucares/pdb/datastore/lang/NewProposerParser.java b/data-store/src/main/java/org/lucares/pdb/datastore/lang/NewProposerParser.java
index c1b21fe..f9d8eb2 100644
--- a/data-store/src/main/java/org/lucares/pdb/datastore/lang/NewProposerParser.java
+++ b/data-store/src/main/java/org/lucares/pdb/datastore/lang/NewProposerParser.java
@@ -19,6 +19,8 @@ public class NewProposerParser {
 
 	private static final Logger LOGGER = LoggerFactory.getLogger(NewProposerParser.class);
 
+	private final static Logger METRICS_LOGGER_PROPOSE = LoggerFactory.getLogger("org.lucares.metrics.propose");
+
 	public final static String CARET_MARKER = "\ue001"; // character in the private use area
 
 	/*
@@ -35,6 +37,7 @@ public class NewProposerParser {
 	}
 
 	public List<Proposal> propose(final String query, final int caretIndex) {
+		final long start = System.nanoTime();
 		List<Proposal> proposals;
 		if (StringUtils.isBlank(query)) {
 			proposals = proposeForAllKeys();
@@ -47,6 +50,8 @@ public class NewProposerParser {
 				proposals = foundProposals;
 			}
 		}
+		METRICS_LOGGER_PROPOSE.debug("compute proposals took {}ms for query '{}' ",
+				(System.nanoTime() - start) / 1_000_000.0, query);
 
 		return proposals;
 	}
diff --git a/data-store/src/main/java/org/lucares/pdb/datastore/lang/QueryCompletionExpressionOptimizer.java b/data-store/src/main/java/org/lucares/pdb/datastore/lang/QueryCompletionExpressionOptimizer.java
index 3701b74..159b134 100644
--- a/data-store/src/main/java/org/lucares/pdb/datastore/lang/QueryCompletionExpressionOptimizer.java
+++ b/data-store/src/main/java/org/lucares/pdb/datastore/lang/QueryCompletionExpressionOptimizer.java
@@ -12,6 +12,8 @@ import org.lucares.pdb.datastore.lang.Expression.Not;
 import org.lucares.pdb.datastore.lang.Expression.Or;
 import org.lucares.pdb.datastore.lang.Expression.Property;
 import org.lucares.pdb.datastore.lang.Expression.Terminal;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * Query completion utilizes an index that contains all mappings of
@@ -43,6 +45,8 @@ import org.lucares.pdb.datastore.lang.Expression.Terminal;
  */
 public class QueryCompletionExpressionOptimizer {
 
+	private static final Logger LOGGER = LoggerFactory.getLogger(QueryCompletionExpressionOptimizer.class);
+
 	private static final class ReplaceINExpressionsWithPropertyExpressionsVisitor extends IdentityExpressionVisitor {
 
 		@Override
@@ -256,9 +260,9 @@ public class QueryCompletionExpressionOptimizer {
 			previousExpression = result;
 			result = previousExpression.visit(visitor);
 			if (!previousExpression.equals(result)) {
-				System.out.println(" translate: " + visitor.getClass().getSimpleName());
-				System.out.println("           in:  " + previousExpression);
-				System.out.println("           out: " + result);
+				LOGGER.debug(" translate: {}", visitor.getClass().getSimpleName());
+				LOGGER.debug("           in:  {}", previousExpression);
+				LOGGER.debug("           out: {}", result);
 			}
 		} while (!previousExpression.equals(result));
 
diff --git a/data-store/src/main/java/org/lucares/pdb/datastore/lang/QueryLanguage.java b/data-store/src/main/java/org/lucares/pdb/datastore/lang/QueryLanguage.java
index cdf7ca5..c849d1c 100644
--- a/data-store/src/main/java/org/lucares/pdb/datastore/lang/QueryLanguage.java
+++ b/data-store/src/main/java/org/lucares/pdb/datastore/lang/QueryLanguage.java
@@ -48,8 +48,6 @@ public class QueryLanguage {
 
 			@Override
 			public void exitIdentifierExpression(final IdentifierExpressionContext ctx) {
-				// System.out.println("push identifier " + ctx.getText());
-
 				if (ctx.getText().length() > 255) {
 					throw new SyntaxException(ctx, "token too long");
 				}