Use PipedIn/Out to reduce heap mem load

src/main/java/eu/dissco/core/translator/repository/BatchInserter.java

@@ -2,9 +2,10 @@
 
 import com.fasterxml.jackson.databind.JsonNode;
 import eu.dissco.core.translator.exception.DisscoRepositoryException;
-import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
+import java.io.PipedInputStream;
+import java.io.PipedOutputStream;
 import java.nio.charset.StandardCharsets;
 import java.sql.SQLException;
 import java.util.List;
@@ -21,22 +22,6 @@ public class BatchInserter {
 
   private final CopyManager copyManager;
 
-  public void batchCopy(String tableName, List<Pair<String, JsonNode>> dbRecords)
-      throws DisscoRepositoryException {
-    try (var outputStream = new ByteArrayOutputStream()) {
-      for (var dbRecord : dbRecords) {
-        outputStream.write(getCsvRow(dbRecord));
-      }
-      var inputStream = new ByteArrayInputStream(outputStream.toByteArray());
-      copyManager.copyIn("COPY " + tableName
-          + " FROM stdin DELIMITER ','", inputStream);
-    } catch (IOException | SQLException e) {
-      throw new DisscoRepositoryException(
-          String.format("An error has occurred inserting %d records into temp table %s",
-              dbRecords.size(), tableName), e);
-    }
-  }
-
   private static byte[] getCsvRow(Pair<String, JsonNode> dbRecord) {
     return (dbRecord.getLeft() + "," +
         cleanString(dbRecord.getRight())
@@ -54,4 +39,31 @@ private static String cleanString(JsonNode jsonNode) {
     return node;
   }
 
+  public void batchCopy(String tableName, List<Pair<String, JsonNode>> dbRecords)
+      throws DisscoRepositoryException {
+    try (var outputStream = new ByteArrayOutputStream();
+        var in = new PipedInputStream();
+        var out = new PipedOutputStream(in)) {
+      for (var dbRecord : dbRecords) {
+        outputStream.write(getCsvRow(dbRecord));
+      }
+      try (in) {
+        new Thread(() -> {
+          try (out) {
+            outputStream.writeTo(out);
+          } catch (IOException e) {
+            log.error("Error writing to pipe", e);
+          }
+        }).start();
+
+        copyManager.copyIn("COPY " + tableName
+            + " FROM stdin DELIMITER ','", in);
+      }
+    } catch (IOException | SQLException e) {
+      throw new DisscoRepositoryException(
+          String.format("An error has occurred inserting %d records into temp table %s",
+              dbRecords.size(), tableName), e);
+    }
+  }
+
 }