diff --git a/pdb-api/src/main/java/org/lucares/pdb/api/Entries.java b/pdb-api/src/main/java/org/lucares/pdb/api/Entries.java
index 6c8c8f6..7cd354b 100644
--- a/pdb-api/src/main/java/org/lucares/pdb/api/Entries.java
+++ b/pdb-api/src/main/java/org/lucares/pdb/api/Entries.java
@@ -5,7 +5,24 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.Iterator;
 import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
 
+/**
+ * Wrapper for chunk of {@link Entry}s.
+ * <p>
+ * This class is supposed to be provided to the queue returned by
+ * PerformanceDb.getQueue(). Processing {@link Entry}s in chunks is more
+ * efficient than processing each one individually.
+ * <p>
+ * Optionally, you can request that the entries will be flushed to disk by
+ * calling {@link #forceFlush()} before adding it to the queue.
+ * <p>
+ * Optionally, this class can act like a future. This is useful if you have to
+ * wait until the entries have been processed. Use {@link #forceFlush()} and
+ * {@link #waitUntilFlushed(long, TimeUnit)}.
+ */
 public class Entries implements Iterable<Entry> {
     /**
      * A special {@link Entries} instance that can be used as poison object for
@@ -15,6 +32,10 @@ public class Entries implements Iterable<Entry> {
 
     private final List<Entry> entries;
 
+    private boolean forceFlush = false;
+
+    private CountDownLatch flushLatch = null;
+
     public Entries(final int initialSize) {
         entries = new ArrayList<>(initialSize);
     }
@@ -39,4 +60,25 @@ public class Entries implements Iterable<Entry> {
     public int size() {
         return entries.size();
     }
+
+    public boolean isForceFlush() {
+        return forceFlush;
+    }
+
+    public void forceFlush() {
+        forceFlush = true;
+        flushLatch = new CountDownLatch(1);
+    }
+
+    public void waitUntilFlushed(final long timeout, final TimeUnit unit)
+            throws InterruptedException, TimeoutException {
+        final boolean finished = flushLatch.await(timeout, unit);
+        if (!finished) {
+            throw new TimeoutException();
+        }
+    }
+
+    public void notifyFlushed() {
+        flushLatch.countDown();
+    }
 }
diff --git a/pdb-ui/src/main/java/org/lucares/pdbui/CsvToEntryTransformer.java b/pdb-ui/src/main/java/org/lucares/pdbui/CsvToEntryTransformer.java
index 1ddd479..3ee8450 100644
--- a/pdb-ui/src/main/java/org/lucares/pdbui/CsvToEntryTransformer.java
+++ b/pdb-ui/src/main/java/org/lucares/pdbui/CsvToEntryTransformer.java
@@ -4,6 +4,8 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.nio.charset.StandardCharsets;
 import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
 
 import org.lucares.collections.IntList;
 import org.lucares.pdb.api.Entries;
@@ -26,7 +28,7 @@ class CsvToEntryTransformer {
         this.settings = settings;
     }
 
-    void readCSV(final InputStream in) throws IOException, InterruptedException {
+    void readCSV(final InputStream in) throws IOException, InterruptedException, TimeoutException {
         final int chunksize = 1000;
         Entries entries = new Entries(chunksize);
 
@@ -93,7 +95,9 @@ class CsvToEntryTransformer {
         if (entry != null) {
             entries.add(entry);
         }
+        entries.forceFlush();
         queue.put(entries);
+        entries.waitUntilFlushed(5, TimeUnit.MINUTES);
     }
 
     private int[] handleCsvHeaderLine(final byte[] line, final int bytesInLine, final IntList separatorPositions) {
diff --git a/pdb-ui/src/main/java/org/lucares/pdbui/CsvUploadHandler.java b/pdb-ui/src/main/java/org/lucares/pdbui/CsvUploadHandler.java
index 423d4c9..c70fa80 100644
--- a/pdb-ui/src/main/java/org/lucares/pdbui/CsvUploadHandler.java
+++ b/pdb-ui/src/main/java/org/lucares/pdbui/CsvUploadHandler.java
@@ -9,9 +9,12 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.UUID;
 import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
 
 import org.lucares.pdb.api.Entries;
 import org.lucares.performance.db.PerformanceDb;
@@ -41,8 +44,9 @@ public class CsvUploadHandler implements PropertyKeys, DisposableBean {
         this.performanceDb = performanceDb;
     }
 
-    public void ingest(final List<MultipartFile> files, final CsvReaderSettings settings)
-            throws IllegalStateException, IOException {
+    public void ingest(final List<MultipartFile> files, final CsvReaderSettings settings,
+            final boolean waitUntilFinished)
+            throws IllegalStateException, IOException, InterruptedException, ExecutionException, TimeoutException {
 
         final List<Path> tmpFiles = new ArrayList<Path>();
 
@@ -58,7 +62,7 @@ public class CsvUploadHandler implements PropertyKeys, DisposableBean {
             throw e;
         }
 
-        threadPool.submit(() -> {
+        final Future<?> future = threadPool.submit(() -> {
             final ArrayBlockingQueue<Entries> queue = performanceDb.getQueue();
             for (final Path tmpFile : tmpFiles) {
                 try {
@@ -74,8 +78,10 @@ public class CsvUploadHandler implements PropertyKeys, DisposableBean {
                     LOGGER.error("csv ingestion failed", e);
                 }
             }
-            queue.add(Entries.POISON);
         });
+        if (waitUntilFinished) {
+            future.get(1, TimeUnit.HOURS);
+        }
     }
 
     @Override
diff --git a/pdb-ui/src/main/java/org/lucares/pdbui/IngestionHandler.java b/pdb-ui/src/main/java/org/lucares/pdbui/IngestionHandler.java
index 795ce26..72f3ae7 100644
--- a/pdb-ui/src/main/java/org/lucares/pdbui/IngestionHandler.java
+++ b/pdb-ui/src/main/java/org/lucares/pdbui/IngestionHandler.java
@@ -12,6 +12,7 @@ import java.nio.charset.StandardCharsets;
 import java.util.Optional;
 import java.util.concurrent.ArrayBlockingQueue;
 import java.util.concurrent.Callable;
+import java.util.concurrent.TimeoutException;
 import java.util.zip.GZIPInputStream;
 
 import org.lucares.pdb.api.Entries;
@@ -50,7 +51,7 @@ public final class IngestionHandler implements Callable<Void> {
         return null;
     }
 
-    private void handleInputStream(final InputStream in) throws IOException, InterruptedException {
+    private void handleInputStream(final InputStream in) throws IOException, InterruptedException, TimeoutException {
         in.mark(1);
         final byte firstByte = (byte) in.read();
         if (firstByte == '{') {
diff --git a/pdb-ui/src/main/java/org/lucares/pdbui/PdbController.java b/pdb-ui/src/main/java/org/lucares/pdbui/PdbController.java
index 4747358..d4ca225 100644
--- a/pdb-ui/src/main/java/org/lucares/pdbui/PdbController.java
+++ b/pdb-ui/src/main/java/org/lucares/pdbui/PdbController.java
@@ -12,7 +12,9 @@ import java.util.Locale;
 import java.util.Set;
 import java.util.SortedSet;
 import java.util.TreeSet;
+import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
 import java.util.concurrent.locks.ReentrantLock;
 import java.util.regex.Pattern;
 
@@ -327,10 +329,11 @@ public class PdbController implements HardcodedValues, PropertyKeys {
     @ResponseBody
     @ResponseStatus(code = HttpStatus.CREATED)
     public String handleCsvFileUpload(@RequestParam("file") final MultipartFile[] files,
-            @RequestPart("settings") final CsvReaderSettings csvReaderSettings)
-            throws IllegalStateException, IOException {
+            @RequestPart("settings") final CsvReaderSettings csvReaderSettings,
+            @RequestParam(name = "waitUntilFinished", defaultValue = "false") final boolean waitUntilFinished)
+            throws IllegalStateException, IOException, InterruptedException, ExecutionException, TimeoutException {
 
-        csvUploadHandler.ingest(List.of(files), csvReaderSettings);
+        csvUploadHandler.ingest(List.of(files), csvReaderSettings, waitUntilFinished);
         return ""; // return value might become a job id that can be used to cancel, or observe
                    // status
     }
diff --git a/pdb-ui/src/test/java/org/lucares/pdbui/CsvToEntryTransformerTest.java b/pdb-ui/src/test/java/org/lucares/pdbui/CsvToEntryTransformerTest.java
index 989160e..489645e 100644
--- a/pdb-ui/src/test/java/org/lucares/pdbui/CsvToEntryTransformerTest.java
+++ b/pdb-ui/src/test/java/org/lucares/pdbui/CsvToEntryTransformerTest.java
@@ -10,8 +10,10 @@ import java.time.format.DateTimeFormatter;
 import java.time.temporal.ChronoUnit;
 import java.util.List;
 import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.TimeoutException;
 
 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.lucares.collections.LongList;
@@ -19,7 +21,6 @@ import org.lucares.pdb.api.DateTimeRange;
 import org.lucares.pdb.api.Entries;
 import org.lucares.pdb.api.Query;
 import org.lucares.performance.db.PerformanceDb;
-import org.junit.jupiter.api.Assertions;
 import org.lucares.utils.file.FileUtils;
 
 public class CsvToEntryTransformerTest {
@@ -37,7 +38,7 @@ public class CsvToEntryTransformerTest {
     }
 
     @Test
-    public void testIngest() throws IOException, InterruptedException {
+    public void testIngest() throws IOException, InterruptedException, TimeoutException {
         final OffsetDateTime dateA = OffsetDateTime.now();
         final OffsetDateTime dateB = OffsetDateTime.now();
 
@@ -75,9 +76,10 @@ public class CsvToEntryTransformerTest {
      * 
      * @throws IOException
      * @throws InterruptedException
+     * @throws TimeoutException
      */
     @Test
-    public void testIgnoreColumns() throws IOException, InterruptedException {
+    public void testIgnoreColumns() throws IOException, InterruptedException, TimeoutException {
 
         try (final PerformanceDb db = new PerformanceDb(dataDirectory)) {
 
diff --git a/pdb-ui/src/test/java/org/lucares/pdbui/PdbControllerTest.java b/pdb-ui/src/test/java/org/lucares/pdbui/PdbControllerTest.java
index eedb2ae..53af5ef 100644
--- a/pdb-ui/src/test/java/org/lucares/pdbui/PdbControllerTest.java
+++ b/pdb-ui/src/test/java/org/lucares/pdbui/PdbControllerTest.java
@@ -4,10 +4,10 @@ import java.time.OffsetDateTime;
 import java.time.format.DateTimeFormatter;
 import java.time.temporal.ChronoUnit;
 import java.util.List;
-import java.util.concurrent.TimeUnit;
 
 import org.apache.logging.log4j.Level;
 import org.apache.logging.log4j.core.config.Configurator;
+import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.lucares.collections.LongList;
@@ -15,7 +15,6 @@ import org.lucares.pdb.api.DateTimeRange;
 import org.lucares.pdb.api.GroupResult;
 import org.lucares.pdb.api.Query;
 import org.lucares.performance.db.PerformanceDb;
-import org.junit.jupiter.api.Assertions;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
@@ -60,7 +59,6 @@ public class PdbControllerTest {
 
         final CsvReaderSettings settings = CsvReaderSettings.create(timeColumn, ',', ignoredColumn);
         uploadCsv(settings, csv);
-        TimeUnit.SECONDS.sleep(1);
         {
             final GroupResult groupResult = performanceDb.get(new Query("tag=tagValue", DateTimeRange.ofDay(dateA)))
                     .singleGroup();
@@ -96,7 +94,8 @@ public class PdbControllerTest {
         final HttpEntity<MultiValueMap<String, Object>> entity = new HttpEntity<MultiValueMap<String, Object>>(
                 parameters, headers);
 
-        final ResponseEntity<String> response = rest.exchange("/data", HttpMethod.POST, entity, String.class);
+        final ResponseEntity<String> response = rest.exchange("/data?waitUntilFinished=true", HttpMethod.POST, entity,
+                String.class);
 
         Assertions.assertEquals(response.getStatusCode(), HttpStatus.CREATED, "response status");
     }
diff --git a/performanceDb/src/main/java/org/lucares/performance/db/PerformanceDb.java b/performanceDb/src/main/java/org/lucares/performance/db/PerformanceDb.java
index 20f7cf8..20a7b2b 100644
--- a/performanceDb/src/main/java/org/lucares/performance/db/PerformanceDb.java
+++ b/performanceDb/src/main/java/org/lucares/performance/db/PerformanceDb.java
@@ -134,6 +134,12 @@ public class PerformanceDb implements AutoCloseable {
                         LOGGER.info("", e);
                     }
                 }
+
+                if (entries.isForceFlush()) {
+                    LOGGER.info("flush triggered via entries.isForceFlush()");
+                    dataStore.flush();
+                    entries.notifyFlushed();
+                }
             }
 
         } catch (final RuntimeException e) {