如何提高Java中的选择查询性能？

Question

I am using BerkeleyDB Database and I am performing select query that require 409 ms. How to improve the select query performance?

I am using the following code:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class ReadData {

Connection con=null;
ResultSet rs=null;
Statement smt = null;

public void readData() 
{
     try
     {
         Class.forName("SQLite.JDBCDriver");
         con = DriverManager.getConnection("jdbc:sqlite:/D:\\DB\\Mediation.db");
         smt = con.createStatement();

         long startTime = System.currentTimeMillis();
         rs = smt.executeQuery("select * from CDRData");             
         while(rs.next())
         {
             System.out.println(rs.getString(1)+" , "+rs.getString(2)+" , "+rs.getString(3)+" , "+rs.getString(4)+" , "+rs.getString(5)+" , "+rs.getString(6)+" , "+rs.getString(7)+" , "+rs.getString(8)+" , "+rs.getString(9)+" , "+rs.getString(10)+" , "+rs.getString(11)+" , "+rs.getString(12)+" , "+rs.getString(13)+" , "+rs.getString(14)+" , "+rs.getString(15)+" , "+rs.getString(16)+" , "+rs.getString(17)+" , "+rs.getString(18)+" , "+rs.getString(19)+" , "+rs.getString(20)+" , "+rs.getString(21)+" , "+rs.getString(22)+" , "+rs.getString(23));
         }
         long finishTime = System.currentTimeMillis();
         System.out.println("The time taken by select query : "+(finishTime-startTime)+ " ms");
     }
     catch(Exception e)
     {
         System.out.println("Error ---- "+e);
     }
}

public static void main(String[] args) {
    ReadData csvread = new ReadData();
    csvread.readData();
}
}

Answer 1

@Dhananjay乔希我的第一recomendation它是由需要该改变的选择select * ，并把你确实需要当你做一个字段select *您带来了很多，也许你并不需要的字段，需要更多的内存

Answer 2

In general terms when using JDBC you may see a performance increase by

• using a StoredProcedure - this elimentates some pre-processing by the database engine
• using a PreparedStatement - this can elimenate some pre-processing if you are using a query multiple times.

You can also improve time by optimising your query, perhaps by adding appropriate indexes. Using explain can help you understand the actions and cost that the query will ancounter.

However, in your example you are just executing a simple select with no predicate, so none of these will help you.

Answer 3

I don't think there is anything to improve with your code in terms of DB access. Selecting all rows is a trivial task for a database which basically just takes a certain amount of time. using a PreparedStatement would give you some improvement, if you repeatedly have the same/similar queries, but not in your test scenario.

You have a little overhead in your java part though which comes from allocating/concatenating string objects. You might replace your loop body by

 System.out.print(rs.getString(1));
 System.out.print(", ");
 System.out.print(rs.getString(2))
 // ...

or a StringBuilder...

Answer 4

Most of the time could be spent printing the results.

Try running the test without printing the data.

Answer 5

You may put a printed timestamp after the "executeQuery" statement. And trying to figure out what spends more time in your program (retrive data from database or java instructions).

Theoretically, retrieving data from database would be the bottleneck if the data is large enough.