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 dba14ac..a53019e 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
@@ -61,6 +61,48 @@ public class DataStore implements AutoCloseable {
 
     public static Tag TAG_ALL_DOCS = null;
 
+    private static final class PartitionedTagsCacheKey {
+        private final Tags tags;
+        private final ParititionId partitionId;
+
+        public PartitionedTagsCacheKey(final Tags tags, final ParititionId partitionId) {
+            super();
+            this.tags = tags;
+            this.partitionId = partitionId;
+        }
+
+        @Override
+        public int hashCode() {
+            final int prime = 31;
+            int result = 1;
+            result = prime * result + ((partitionId == null) ? 0 : partitionId.hashCode());
+            result = prime * result + ((tags == null) ? 0 : tags.hashCode());
+            return result;
+        }
+
+        @Override
+        public boolean equals(final Object obj) {
+            if (this == obj)
+                return true;
+            if (obj == null)
+                return false;
+            if (getClass() != obj.getClass())
+                return false;
+            final PartitionedTagsCacheKey other = (PartitionedTagsCacheKey) obj;
+            if (partitionId == null) {
+                if (other.partitionId != null)
+                    return false;
+            } else if (!partitionId.equals(other.partitionId))
+                return false;
+            if (tags == null) {
+                if (other.tags != null)
+                    return false;
+            } else if (!tags.equals(other.tags))
+                return false;
+            return true;
+        }
+    }
+
     private final PartitionPersistentMap<Long, Doc, Doc> docIdToDoc;
 
     private final PartitionPersistentMap<Tags, Long, Long> tagsToDocId;
@@ -73,7 +115,7 @@ public class DataStore implements AutoCloseable {
     // easily.
     private final HotEntryCache<Long, Doc> docIdToDocCache = new HotEntryCache<>(Duration.ofMinutes(30), 100_000);
 
-    private final HotEntryCache<Tags, PdbWriter> writerCache;
+    private final HotEntryCache<PartitionedTagsCacheKey, PdbWriter> writerCache;
 
     private final PartitionDiskStore diskStorage;
     private final Path storageBasePath;
@@ -328,7 +370,8 @@ public class DataStore implements AutoCloseable {
 
     private PdbWriter getWriter(final ParititionId partitionId, final Tags tags) throws ReadException, WriteException {
 
-        return writerCache.putIfAbsent(tags, t -> getWriterInternal(partitionId, tags));
+        final PartitionedTagsCacheKey cacheKey = new PartitionedTagsCacheKey(tags, partitionId);
+        return writerCache.putIfAbsent(cacheKey, t -> getWriterInternal(partitionId, tags));
     }
 
     // visible for test
diff --git a/data-store/src/main/java/org/lucares/pdb/datastore/internal/PartitionLongList.java b/data-store/src/main/java/org/lucares/pdb/datastore/internal/PartitionLongList.java
index e16377c..33b40c0 100644
--- a/data-store/src/main/java/org/lucares/pdb/datastore/internal/PartitionLongList.java
+++ b/data-store/src/main/java/org/lucares/pdb/datastore/internal/PartitionLongList.java
@@ -92,4 +92,23 @@ public class PartitionLongList implements Iterable<ParititionId> {
             }
         }
     }
+
+    @Override
+    public String toString() {
+        final StringBuilder builder = new StringBuilder();
+        for (final ParititionId partitionId : lists.keySet()) {
+            builder.append(partitionId.getPartitionId());
+            builder.append(": values=");
+            final LongList longList = lists.get(partitionId);
+            builder.append(longList.size());
+            if (longList.size() > 0) {
+                builder.append(" first=");
+                builder.append(longList.get(0));
+                builder.append(" last=");
+                builder.append(longList.get(longList.size() - 1));
+            }
+        }
+        return builder.toString();
+    }
+
 }
diff --git a/pdb-ui/src/test/java/org/lucares/pdbui/TcpIngestorTest.java b/pdb-ui/src/test/java/org/lucares/pdbui/TcpIngestorTest.java
index 8a72d2b..897a0a0 100644
--- a/pdb-ui/src/test/java/org/lucares/pdbui/TcpIngestorTest.java
+++ b/pdb-ui/src/test/java/org/lucares/pdbui/TcpIngestorTest.java
@@ -17,6 +17,7 @@ import java.util.concurrent.LinkedBlockingDeque;
 import java.util.concurrent.ThreadLocalRandom;
 
 import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
@@ -27,7 +28,6 @@ import org.lucares.pdb.api.Query;
 import org.lucares.pdb.datastore.internal.DataStore;
 import org.lucares.performance.db.PdbExport;
 import org.lucares.performance.db.PerformanceDb;
-import org.junit.jupiter.api.Assertions;
 import org.lucares.utils.file.FileUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -311,4 +311,49 @@ public class TcpIngestorTest {
             Assertions.assertEquals(value2, result.get(3));
         }
     }
+
+    @Test
+    public void testCsvIngestorWithEventsFromDifferentMonths() throws Exception {
+
+        final String host = "someHost";
+        final long value1 = 222;
+        final long value2 = 1;
+
+        final OffsetDateTime dateNovember = OffsetDateTime.of(2019, 11, 30, 23, 59, 59, 999, ZoneOffset.UTC);
+        final OffsetDateTime dateDecember = OffsetDateTime.of(2019, 12, 1, 0, 0, 0, 0, ZoneOffset.UTC);
+
+        try (TcpIngestor ingestor = new TcpIngestor(dataDirectory)) {
+
+            ingestor.start();
+
+            final Map<String, Object> entry1 = new HashMap<>();
+            entry1.put("@timestamp", dateNovember.format(DateTimeFormatter.ISO_ZONED_DATE_TIME));
+            entry1.put("host", host);
+            entry1.put("duration", value1);
+
+            final Map<String, Object> entry2 = new HashMap<>();
+            entry2.put("@timestamp", dateDecember.format(DateTimeFormatter.ISO_ZONED_DATE_TIME));
+            entry2.put("host", host);
+            entry2.put("duration", value2);
+
+            PdbTestUtil.sendAsCsv(List.of("@timestamp", "host", "duration"), List.of(entry1, entry2));
+        } catch (final Exception e) {
+            LOGGER.error("", e);
+            throw e;
+        }
+
+        try (PerformanceDb db = new PerformanceDb(dataDirectory)) {
+            final DateTimeRange rangeNovember = new DateTimeRange(dateNovember, dateNovember);
+            final LongList resultNovember = db.get(new Query("host=" + host, rangeNovember)).singleGroup().flatMap();
+            Assertions.assertEquals(2, resultNovember.size());
+            Assertions.assertEquals(dateNovember.toInstant().toEpochMilli(), resultNovember.get(0));
+            Assertions.assertEquals(value1, resultNovember.get(1));
+
+            final DateTimeRange rangeDecember = new DateTimeRange(dateDecember, dateDecember);
+            final LongList resultDecember = db.get(new Query("host=" + host, rangeDecember)).singleGroup().flatMap();
+            Assertions.assertEquals(2, resultDecember.size());
+            Assertions.assertEquals(dateDecember.toInstant().toEpochMilli(), resultDecember.get(0));
+            Assertions.assertEquals(value2, resultDecember.get(1));
+        }
+    }
 }