多线程 java 应用程序中的 SQLite
我编写了一个Java应用程序，它偶尔将事件从多个线程记录到SQLite数据库。我注意到，通过同时生成少量事件，我可以相对容易地触发SQLite的“数据库锁定”错误。这促使我编写了一个模拟最坏情况行为的测试程序，我对SQLite在这个用例中的表现如此之差感到惊讶。下面发布的代码只是将五条记录添加到数据库中，首先按顺序获取“控制”值。然后同时添加相同的五条记录。
import java.sql.*;
public class Main {
public static void main(String[] args) throws Exception {
Class.forName("org.sqlite.JDBC");
Connection conn = DriverManager.getConnection("jdbc:sqlite:test.db");
Statement stat = conn.createStatement();
stat.executeUpdate("drop table if exists people");
stat.executeUpdate("create table people (name, occupation)");
conn.close();
SqlTask tasks[] = {
new SqlTask("Gandhi", "politics"),
new SqlTask("Turing", "computers"),
new SqlTask("Picaso", "artist"),
new SqlTask("shakespeare", "writer"),
new SqlTask("tesla", "inventor"),
};
System.out.println("Sequential DB access:");
Thread threads[] = new Thread[tasks.length];
for(int i = 0; i < tasks.length; i++)
threads[i] = new Thread(tasks[i]);
for(int i = 0; i < tasks.length; i++) {
threads[i].start();
threads[i].join();
}
System.out.println("Concurrent DB access:");
for(int i = 0; i < tasks.length; i++)
threads[i] = new Thread(tasks[i]);
for(int i = 0; i < tasks.length; i++)
threads[i].start();
for(int i = 0; i < tasks.length; i++)
threads[i].join();
}
private static class SqlTask implements Runnable {
String name, occupation;
public SqlTask(String name, String occupation) {
this.name = name;
this.occupation = occupation;
}
public void run() {
Connection conn = null;
PreparedStatement prep = null;
long startTime = System.currentTimeMillis();
try {
try {
conn = DriverManager.getConnection("jdbc:sqlite:test.db");
prep = conn.prepareStatement("insert into people values (?, ?)");
prep.setString(1, name);
prep.setString(2, occupation);
prep.executeUpdate();
long duration = System.currentTimeMillis() - startTime;
System.out.println(" SQL Insert completed: " + duration);
}
finally {
if (prep != null) prep.close();
if (conn != null) conn.close();
}
}
catch(SQLException e) {
long duration = System.currentTimeMillis() - startTime;
System.out.print(" SQL Insert failed: " + duration);
System.out.println(" SQLException: " + e);
}
}
}
}
以下是我运行此java代码时的输出：
[java] Sequential DB access:
[java] SQL Insert completed: 132
[java] SQL Insert completed: 133
[java] SQL Insert completed: 151
[java] SQL Insert completed: 134
[java] SQL Insert completed: 125
[java] Concurrent DB access:
[java] SQL Insert completed: 116
[java] SQL Insert completed: 1117
[java] SQL Insert completed: 2119
[java] SQL Insert failed: 3001 SQLException: java.sql.SQLException: database locked
[java] SQL Insert completed: 3136
按顺序插入 5 条记录大约需要 750 毫秒，我预计并发插入大约需要相同的时间。但是你可以看到，给定3秒的超时，他们甚至不会完成。我还用C语言编写了一个类似的测试程序，使用SQLite的本机库调用，同时插入在与并发插入大致相同的时间内完成。所以问题出在我的java库上。
以下是我运行C版本时的输出：
Sequential DB access:
SQL Insert completed: 126 milliseconds
SQL Insert completed: 126 milliseconds
SQL Insert completed: 126 milliseconds
SQL Insert completed: 125 milliseconds
SQL Insert completed: 126 milliseconds
Concurrent DB access:
SQL Insert completed: 117 milliseconds
SQL Insert completed: 294 milliseconds
SQL Insert completed: 461 milliseconds
SQL Insert completed: 662 milliseconds
SQL Insert completed: 862 milliseconds
我用两个不同的JDBC驱动程序（http://www.zentus.com/sqlitejdbc 和 http://www.xerial.org/trac/Xerial/wiki/SQLiteJDBC）和sqlite4java包装器尝试了这段代码。每次结果都是相似的。有没有人知道一个没有这种行为的Java的SQLite库？
