diff --git a/data-store/src/main/java/org/lucares/pdb/datastore/internal/ClusterIdSource.java b/data-store/src/main/java/org/lucares/pdb/datastore/internal/ClusterIdSource.java
new file mode 100644
index 0000000..7916e71
--- /dev/null
+++ b/data-store/src/main/java/org/lucares/pdb/datastore/internal/ClusterIdSource.java
@@ -0,0 +1,7 @@
+package org.lucares.pdb.datastore.internal;
+
+import java.util.List;
+
+public interface ClusterIdSource {
+	List<ClusterId> toClusterIds();
+}
diff --git a/data-store/src/main/java/org/lucares/pdb/datastore/internal/ClusteredPersistentMap.java b/data-store/src/main/java/org/lucares/pdb/datastore/internal/ClusteredPersistentMap.java
index 519a879..a58018b 100644
--- a/data-store/src/main/java/org/lucares/pdb/datastore/internal/ClusteredPersistentMap.java
+++ b/data-store/src/main/java/org/lucares/pdb/datastore/internal/ClusteredPersistentMap.java
@@ -1,14 +1,17 @@
 package org.lucares.pdb.datastore.internal;
 
 import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.function.Function;
 
-import org.lucares.pdb.api.DateTimeRange;
+import org.lucares.pdb.api.RuntimeIOException;
 import org.lucares.pdb.datastore.ReadRuntimeException;
 import org.lucares.pdb.map.PersistentMap;
+import org.lucares.pdb.map.PersistentMap.EncoderDecoder;
 import org.lucares.pdb.map.Visitor;
 
 public class ClusteredPersistentMap<K, V> implements AutoCloseable {
@@ -16,27 +19,46 @@ public class ClusteredPersistentMap<K, V> implements AutoCloseable {
 	private final ConcurrentHashMap<ClusterId, PersistentMap<K, V>> maps = new ConcurrentHashMap<>();
 
 	private final Function<ClusterId, PersistentMap<K, V>> creator;
+	private final Function<ClusterId, PersistentMap<K, V>> supplier;
 
-	// TODO we need two creators, one that actually creates a new map and one that
-	// only creates a new map if the file on disk already exists
-	public ClusteredPersistentMap(final Function<ClusterId, PersistentMap<K, V>> creator) {
-		this.creator = (dateIndexPrefix) -> creator.apply(dateIndexPrefix);
+	public ClusteredPersistentMap(final Path storageBasePath, final String filename, final EncoderDecoder<K> keyEncoder,
+			final EncoderDecoder<V> valueEncoder) {
+
+		creator = clusterId -> {
+			try {
+				final Path file = storageBasePath.resolve(clusterId.getClusterId()).resolve(filename);
+				return new PersistentMap<>(file, keyEncoder, valueEncoder);
+			} catch (final IOException e) {
+				throw new RuntimeIOException(e);
+			}
+		};
+		supplier = clusterId -> {
+			try {
+				final Path file = storageBasePath.resolve(clusterId.getClusterId()).resolve(filename);
+				if (Files.exists(file)) {
+					return new PersistentMap<>(file, keyEncoder, valueEncoder);
+				}
+				return null;
+			} catch (final IOException e) {
+				throw new RuntimeIOException(e);
+			}
+		};
 	}
 
 	public V getValue(final ClusterId clusterId, final K key) {
 		try {
 
-			final PersistentMap<K, V> map = maps.computeIfAbsent(clusterId, creator);
+			final PersistentMap<K, V> map = maps.computeIfAbsent(clusterId, supplier);
 			return map != null ? map.getValue(key) : null;
 		} catch (final IOException e) {
 			throw new ReadRuntimeException(e);
 		}
 	}
 
-	public List<V> getValues(final DateTimeRange dateRange, final K key) {
+	public List<V> getValues(final ClusterIdSource clusterIdSource, final K key) {
 		try {
 			final List<V> result = new ArrayList<>();
-			final List<ClusterId> clusterIds = DateIndexExtension.toClusterIds(dateRange);
+			final List<ClusterId> clusterIds = clusterIdSource.toClusterIds();
 
 			for (final ClusterId clusterId : clusterIds) {
 				final PersistentMap<K, V> map = maps.computeIfAbsent(clusterId, creator);
@@ -75,9 +97,9 @@ public class ClusteredPersistentMap<K, V> implements AutoCloseable {
 		}
 	}
 
-	public void visitValues(final DateTimeRange dateRange, final K keyPrefix, final Visitor<K, V> visitor) {
+	public void visitValues(final ClusterIdSource clusterIdSource, final K keyPrefix, final Visitor<K, V> visitor) {
 		try {
-			final List<ClusterId> clusterIds = DateIndexExtension.toClusterIds(dateRange);
+			final List<ClusterId> clusterIds = clusterIdSource.toClusterIds();
 
 			for (final ClusterId clusterId : clusterIds) {
 				final PersistentMap<K, V> map = maps.get(clusterId);
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 c7447b8..fd7aa22 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
@@ -94,33 +94,14 @@ public class DataStore implements AutoCloseable {
 		diskStorage = new DiskStorage(diskStorageFilePath);
 		diskStorage.ensureAlignmentForNewBlocks(BSFile.BLOCK_SIZE);
 
-		tagToDocsId = new ClusteredPersistentMap<>(clusterId -> {
-			try {
-				final Path file = storageBasePath.resolve(clusterId.getClusterId())
-						.resolve("keyToValueToDocIdsIndex.bs");
-				return new PersistentMap<>(file, new TagEncoderDecoder(), PersistentMap.LONG_CODER);
-			} catch (final IOException e) {
-				throw new RuntimeIOException(e);
-			}
-		});
+		tagToDocsId = new ClusteredPersistentMap<>(storageBasePath, "keyToValueToDocIdsIndex.bs",
+				new TagEncoderDecoder(), PersistentMap.LONG_CODER);
 
-		tagsToDocId = new ClusteredPersistentMap<>(clusterId -> {
-			try {
-				final Path file = storageBasePath.resolve(clusterId.getClusterId()).resolve("tagsToDocIdIndex.bs");
-				return new PersistentMap<>(file, new TagsEncoderDecoder(), PersistentMap.LONG_CODER);
-			} catch (final IOException e) {
-				throw new RuntimeIOException(e);
-			}
-		});
+		tagsToDocId = new ClusteredPersistentMap<>(storageBasePath, "tagsToDocIdIndex.bs", new TagsEncoderDecoder(),
+				PersistentMap.LONG_CODER);
 
-		docIdToDoc = new ClusteredPersistentMap<>(clusterId -> {
-			try {
-				final Path file = storageBasePath.resolve(clusterId.getClusterId()).resolve("docIdToDocIndex.bs");
-				return new PersistentMap<>(file, PersistentMap.LONG_CODER, new DocEncoderDecoder());
-			} catch (final IOException e) {
-				throw new RuntimeIOException(e);
-			}
-		});
+		docIdToDoc = new ClusteredPersistentMap<>(storageBasePath, "docIdToDocIndex.bs", PersistentMap.LONG_CODER,
+				new DocEncoderDecoder());
 
 		queryCompletionIndex = new QueryCompletionIndex(storageBasePath);
 
@@ -251,7 +232,8 @@ public class DataStore implements AutoCloseable {
 
 		final Tag keyPrefix = new Tag("", ""); // will find everything
 
-		tagToDocsId.visitValues(dateRange, keyPrefix, (tags, __) -> keys.add(tags.getKeyAsString()));
+		final ClusterIdSource clusterIdSource = new DateCluster(dateRange);
+		tagToDocsId.visitValues(clusterIdSource, keyPrefix, (tags, __) -> keys.add(tags.getKeyAsString()));
 
 		keys.remove(ALL_DOCS_KEY);
 		final List<String> result = new ArrayList<>(keys);
@@ -264,8 +246,8 @@ public class DataStore implements AutoCloseable {
 
 		final SortedSet<String> result = new TreeSet<>();
 		if (query.getQuery().isEmpty()) {
-			tagToDocsId.visitValues(query.getDateRange(), new Tag(key, ""),
-					(tag, __) -> result.add(tag.getValueAsString()));
+			final ClusterIdSource clusterIdSource = new DateCluster(query.getDateRange());
+			tagToDocsId.visitValues(clusterIdSource, new Tag(key, ""), (tag, __) -> result.add(tag.getValueAsString()));
 		} else {
 			final List<Doc> docs = search(query);
 			for (final Doc doc : docs) {
@@ -327,7 +309,8 @@ public class DataStore implements AutoCloseable {
 	public List<Doc> getByTags(final DateTimeRange dateRange, final Tags tags) {
 
 		final List<Doc> result = new ArrayList<>();
-		final List<Long> docIds = tagsToDocId.getValues(dateRange, tags);
+		final DateCluster dateCluster = new DateCluster(dateRange);
+		final List<Long> docIds = tagsToDocId.getValues(dateCluster, tags);
 		for (final Long docId : docIds) {
 
 			if (docId != null) {
@@ -348,7 +331,8 @@ public class DataStore implements AutoCloseable {
 	private Doc getDocByDocId(final DateTimeRange dateRange, final Long docId) {
 		return docIdToDocCache.putIfAbsent(docId, () -> {
 
-			final List<Doc> docIds = docIdToDoc.getValues(dateRange, docId);
+			final DateCluster dateCluster = new DateCluster(dateRange);
+			final List<Doc> docIds = docIdToDoc.getValues(dateCluster, docId);
 			if (docIds.size() == 1) {
 				return docIds.get(0);
 			} else if (docIds.size() > 1) {
diff --git a/data-store/src/main/java/org/lucares/pdb/datastore/internal/DateCluster.java b/data-store/src/main/java/org/lucares/pdb/datastore/internal/DateCluster.java
new file mode 100644
index 0000000..90df6e7
--- /dev/null
+++ b/data-store/src/main/java/org/lucares/pdb/datastore/internal/DateCluster.java
@@ -0,0 +1,19 @@
+package org.lucares.pdb.datastore.internal;
+
+import java.util.List;
+
+import org.lucares.pdb.api.DateTimeRange;
+
+public class DateCluster implements ClusterIdSource {
+
+	private final DateTimeRange dateRange;
+
+	public DateCluster(final DateTimeRange dateRange) {
+		this.dateRange = dateRange;
+	}
+
+	@Override
+	public List<ClusterId> toClusterIds() {
+		return DateIndexExtension.toClusterIds(dateRange);
+	}
+}