Efficient Techniques For Loading Data Into Memory

Data loading usually has to do with initializing cache data on start up. However, quite often caches need to be loaded or reloaded periodically, and not only on start up. In cases in which you need to load lots of data, either at start up or at any point afterward, using standard cache put(...) or putAll(...) operations is generally inefficient, especially when transactional boundaries are not important. This is especially true when data has to be partitioned across the network, so you don't know in advance on which node the data will end up.

For fast loading of large amounts of data, GridGain provides a cool mechanism called data loader (implemented via GridDataLoader). The data loader will properly batch keys together and collocate those batches with nodes on which the data will be cached. By controlling the size of the batch and the size of internal transactions it is possible to achieve very fast data loading rates.

The code below shows an example of how it can be done:

// Get the data loader reference.
try (GridDataLoader<Integer, String> ldr = grid.dataLoader("partitioned")) {
    // Load the entries.
    for (int i = 0; i < ENTRY_COUNT; i++)
        ldr.addData(i, Integer.toString(i));
}

@Override
public void loadAll(@Nullable String cacheName, 
    GridInClosure2<UUID, Person> closure, Object... args) throws GridException {
    try (Connection conn = getConnection()) {
        // Load all Persons from database (perhaps to warm up cache?)
        try (PreparedStatement st = 
            conn.prepareStatement("select * from PERSONS")) {
            ResultSet rs = st.executeQuery();
  
            while (rs.next())
                c.apply(
                    // Key.
                    UUID.fromString(rs.getString(1)),
                    // New value.
                    person(rs.getString(1), rs.getString(2),
                        rs.getString(3), rs.getString(4))
                );
            }
        }
    }
    catch (SQLException e) {
        throw new GridException("Failed to load objects", e);
    }
}