duration for inserts was wrong

The bug was, that we computed the difference between millis and nanos.
Also log duration for flushes.

performanceDb/src/main/java/org/lucares/performance/db/PerformanceDb.java

@@ -86,7 +86,7 @@ public class PerformanceDb implements AutoCloseable, CollectionUtils {
 					count++;
 
 					if (count % blocksize == 0) {
-						final long end = System.nanoTime();
+						final long end = System.currentTimeMillis();
 						final long duration = end - start;
 						LOGGER.debug("inserting the last " + blocksize + " took " + duration + " ms; total entries: "
 								+ count / 1_000_000.0 + " million");
@@ -95,7 +95,9 @@ public class PerformanceDb implements AutoCloseable, CollectionUtils {
 					}
 
 					if (count % blocksize == 0) {
+						final long startFlush = System.currentTimeMillis();
 						tagsToFile.flush();
+						LOGGER.debug("flushed all files: " + (System.currentTimeMillis() - startFlush) + "ms");
 					}
 
 				} catch (final InvalidValueException e) {