[SOLVED] How can i reduce heap usage for DataNucleus + Derby

How can i reduce heap usage for DataNucleus + Derby

I have a Java desktop application that downloads 700K entries in batches of 50K from a service and stores them in a Derby base

The problem is that this works only if i have set -Xmx1024 otherwise the application crashes with a heap error message. Although the final size of the database is about 100M

Could you please suggest a way to optimize the following code to use less memory

the code for doing the download is pretty much like this

public static final void getItems() {
  ItemsRequest req = new ItemsRequest();
  Gson g = new Gson();
  int next_index_to_read = 0;
  int max_read_entry_count = 50000;
  req.setLimit(max_read_entry_count);
  ItemsResponse resp = null;
  do{
    resp = g.fromJson(postRequest(g.toJson(req)), ItemsResponse.class);
    resp.saveItems();
    next_index_to_read += max_read_entry_count;
    req.setFrom(next_index_to_read);
  }while(resp.getTotalItemsEntryCount()>next_index_to_read);
}

and the code responsible for saving data is

public class ItemsResponse
  public void saveItems() {
    PersistenceManagerFactory pmf = PMF.getPmf();

    PersistenceManager pm = pmf.getPersistenceManager();
    Transaction tx = pm.currentTransaction();

    try {
      tx.begin();

      if (data != null) {
        for (Item item : data) {
          Item item = null;
          try {
            item = pm.getObjectById(Item.class, item.getItemId());
          } catch (Exception e) {
            continue;
          }
          pm.makePersistent(item);
        }
      }
      tx.commit();
    } catch (Exception e) {
      Logger.getLogger("com.example").error("ItemResponse.saveData", e);
    } finally {
      if (tx.isActive()) {
        tx.rollback();
      }
    }
    pm.close();
  }

Solution