H2 performance degrade using remote tcp server - database

Question

I have a simple application that uses a single connection, the flow is something like this:
SELECT QUERY
CONNECTION CLOSE
for(..) //thousands of iterations
{
SIMPLE SELECT QUERY
}
BUSINESS LOGIC
CONNECTION CLOSE
for(..) //thousands of iterations
{
SIMPLE SELECT QUERY
}
BUSINESS LOGIC
CONNECTION CLOSE
When i use the embedded connection mode, the application ends in about 20 seconds, but when i switch to the server mode, the performances deteriorate:
localhost: 110 seconds
remote server (LAN): more than 30 minutes
Each query retrieves a small amount of data.
Is there an explanation for such a poor performance? How can i speed up the application without rewriting the code?
Any help is appreciated

Answer 1

compare your problem like accessing a cup of coffee.
If you access your coffe on your table/workdesk it is comparable like a in memory access to your database (H2 embedded)
It takes about seconds (coffee) and microseconds (h2 embedded)
if you need to go to the kitchen to access a cup of coffe it will take you the travel time from your chair to the kitchen + back (response).
The kitchen is comparable like TCP accessing or file accessing your local database.
It takes you minutes (coffee) and one digit milliseconds (h2 tcp localhost or local file)
if you need to go to a coffeshop outside to access a cup of coffee it will take you at least 15 mins to get a cup of coffee (and ages ( at least 2 digits milliseconds) in h2 tcp on remote machine)
now the question, how many times do you want to travel to a coffeshop?
If I give you a iteration (for loop) over 1000 times to the coffeshop, would you just asking me after the second or the third time if I am kidding? Why do you bother a IO dependent system on long travel times over the network?
So in your case, if you reduce your second for-loop into one SQL query, you will get a great performance locally and of course especially on the remote way.
I hope I could explain you the situation with the coffee, since it explains the problem better.
So to answer the last question, you have to rewrite your "thousands of iterations" for-loops.
Update 1
Forgot, if your for-loops are writing loops (update/insert) you can use batch queries. How to use them depends on your language you are using. Batches are to provide the database a bunch (e.g. multiple hundreds) of insert/updates before the operation takes in place on the database.

Answer 2

I did following test with your provided H2 version.
create a test database with 500.000 records, database size 990 MB
java -cp h2-1.3.168.jar;. PerfH2 create
select random 8.000 records on the indexed column
in embedded mode -> 1.7 sec
java -cp h2-1.3.168.jar;. PerfH2 embedded
in server (localhost) mode -> 2.6 sec
java -cp h2-1.3.168.jar;. PerfH2 server
If you face the problem already using server mode as jdbc:h2:tcp://localhost/your_database, then something with your environment or the way you access the server mode seems to be wrong. Try with a stripped done application and check if the problem still exists. If you have can reproduce the problem also with a stripped down version please post the code.
Find the code used for the test below.
public class PerfH2 {
public static void main(String[] args) throws SQLException {
if (null == args[0]) {
showUsage();
return;
}
long start = System.currentTimeMillis();
switch (args[0]) {
case "create":
createDatabase();
break;
case "embedded":
try (Connection conn = getEmbeddedConnection()) {
execSelects(conn);
}
break;
case "server":
try (Connection conn = getServerConnection()) {
execSelects(conn);
}
break;
default:
showUsage();
}
System.out.printf("duration: %d%n", System.currentTimeMillis() - start);
}
private static Connection getServerConnection() throws SQLException {
return DriverManager.getConnection("jdbc:h2:tcp://localhost/perf_test", "sa", "");
}
private static Connection getEmbeddedConnection() throws SQLException {
return DriverManager.getConnection("jdbc:h2:d:/temp/perf_test", "sa", "");
}
private static void execSelects(final Connection conn) throws SQLException {
Random rand = new Random(1);
String selectSql = "SELECT * FROM TEST_TABLE WHERE ID = ?";
PreparedStatement selectStatement = conn.prepareStatement(selectSql);
int count = 0;
for (int i = 0; i < 8000; i++) {
selectStatement.setInt(1, rand.nextInt(500_000));
ResultSet rs = selectStatement.executeQuery();
while (rs.next()) {
count++;
}
}
System.out.printf("retrieved rows: %d%n", count);
}
private static void createDatabase() throws SQLException {
try (Connection conn = DriverManager.getConnection("jdbc:h2:d:/temp/perf_test", "sa", "")) {
String createTable = "CREATE TABLE TEST_TABLE(ID INT, NAME VARCHAR(1024))";
conn.createStatement().executeUpdate(createTable);
String insertSql = "INSERT INTO TEST_TABLE VALUES(?, ?)";
PreparedStatement insertStmnt = conn.prepareStatement(insertSql);
StringBuilder sb = new StringBuilder(1024);
for (int i = 0; i < 1024 / 10; i++) {
sb.append("[cafebabe]");
}
String value = sb.toString();
int count = 0;
for (int i = 0; i < 50; i++) {
insertStmnt.setInt(1, i);
insertStmnt.setString(2, value);
count += insertStmnt.executeUpdate();
}
System.out.printf("inserted rows: %d%n", count);
conn.commit();
String createIndex = "CREATE INDEX TEST_INDEX ON TEST_TABLE(ID)";
conn.createStatement().executeUpdate(createIndex);
}
}
private static void showUsage() {
System.out.println("usage: PerfH2 [create|embedded|server]");
}
}