hll-java-test.java

final static int SEED = 123456;
final static int LOG2M = 15; // Number of Buckets  = 2^LOG2M
final static int REGWIDTH = 5;
final static int EXPTHRESH = -1;
final static boolean SPARSEON = true;
 
 
/**
 * Generates a HLL Object with numbers from 0 to n the parameter passed
 * @param n : Number of Elements in the HLL.
 * @return Byte Array of the HLL Generated
 */
public static byte[] generateHLLofListOfElements(int n) {
 
    HashFunction hf = Hashing.murmur3_128(HLLTest.SEED);
    HLL hll = new HLL(LOG2M, REGWIDTH, EXPTHRESH, SPARSEON, HLLType.EMPTY);
    for (int i = 0; i < n; ++i) {
        long hashedValue = hf.hashInt(i).asLong();
        hll.addRaw(hashedValue);
    }
    return hll.toBytes();
}
 
 
/**
 * Inserts a row in the hll_test table with HLL in the form of Byte Arrays and app_id
 * @param app_id String Application_id
 * @param user_id_hll Byte Array of the HLL of User Ids
 * @param session_id_hll Byte Array of the HLL of Session Ids
 */
public static void insertHLLByteArrayDB(String app_id, byte[] user_id_hll, byte[] session_id_hll) {
    try {
        PreparedStatement stmt = conn.prepareStatement("INSERT INTO hll_test (page, user_id_hll, session_id_hll) VALUES (?, ?, ?)");
        stmt.setString(1, app_id);
        stmt.setBytes(2, user_id_hll);
        stmt.setBytes(3, session_id_hll);
        stmt.executeUpdate();
        stmt.close();
 
    } catch (SQLException e) {
        System.err.println(e.getClass().getName() + ": " + e.getMessage());
    }
}
 
 
/**
 * Acquires counts of the Unique User ID Count and Session ID Count after merging different rows.
 * @return HashMap of the counts
 */
public static HashMap<String, Long> getGroupedCardinality() {
    HashMap<String, Long> rslt = new HashMap<>();
    try {
        Statement stmt = conn.createStatement();
        String query = "SELECT hll_cardinality(hll_union_agg(user_id_hll :: hll)) as unique_user_count, " +
                "hll_cardinality(hll_union_agg(session_id_hll ::hll)) as unique_session_count  FROM hll_test";
        ResultSet rs = stmt.executeQuery(query);
        rs.next();
        long unique_user_cnt = rs.getLong("unique_user_count");
        long unique_session_cnt = rs.getLong("unique_session_count");
        rslt.put("unique_user_count", unique_user_cnt);
        rslt.put("unique_session_count", unique_session_cnt);
    } catch (SQLException e) {
        System.err.println(e.getClass().getName() + ": " + e.getMessage());
    }
    return rslt;
}