如何在Java应用程序中运行SQLite VACUUM命令？

Question

Question: I want to allow my Java application to manually run the SQLite VACUUM command? I include a code snippet below. I have tried as a PreparedStatement and as a straight Statement. I have also done an extensive web search for a solution and have found no relevant examples.

What Happens? When I run my code, the system pauses. Looking at the directory, the file size does not decrease when executing my code. RecordSet returns false as well.

But, if I run SQLiteManager via Firefox and run Compact Database, the database does compact. NOTE: I make a copy of the DB before compacting so I can see the difference in size.

Sanity Checks --I make sure the DB is closed by all other applications (including SQLiteManager). --No known transactions running. --No exceptions thrown.

Code Snippet: I kept my test code inside. This is NOT production code so error handling etc is available but minimal.

try {
    Connection conn = db.getConnection() ;
    StringBuilder sql = new StringBuilder() ;
    sql.append("VACUUM");

    //PreparedStatement prep = conn.prepareStatement(sql.toString()) ;
    Statement stat = conn.createStatement() ;
    boolean rs = stat.execute(sql.toString()) ;

    System.out.println("Executed vacuum " + rs ) ;     

    //Testing code--preparedstatement attempts
    //conn.setAutoCommit(false);
    //boolean rs = prep.execute() ;
    //conn.setAutoCommit(true);

    } catch (Exception e) {
       //Edited back in after posting to StackOverflow
        System.out.println(
                ".SQLiteVacuum :: exception " + 
                e.getMessage() + " " + e.getClass().getName() );
        e.printStackTrace() ;
    }

Cross References Java 1.6+ SQLite 3+ Xerial JDBC Driver

Addendum

private final String dbJDBCdriverclassname = "org.sqlite.JDBC" ;
private final String dbJDBCpreconnectionstring = "jdbc:sqlite:" ;
        // Setup the driver reference
        Class.forName(dbJDBCdriverclassname) ; //"org.sqlite.JDBC"

        // Create the connection string
        String connstring = dbJDBCpreconnectionstring + this.getDBConnectionFullFileName() ;

        // create the connection
        dbconnection = 
                DriverManager.getConnection(connstring) ; // "jdbc:sqlite:test.db"

Answer 1

I know that this is quite old but if everyone needs here it goes.

Statement stmt = null;
ResultSet rs = null;
try {
    Connection conn = DBConnection.getConnection();//something to get a connection
    stmt = conn.createStatement();
    stmt.executeUpdate("VACUUM");
} catch (SQLException ex) {
    //Something if you like, or not you're the boss!
} finally {
    DBConnection.closeResources(rs, stmt);//something to close all the resources
}

With something like this snippet, I got 63KB of savings in a test DataBase of 185KB.

Answer 2

Are you using the correct driver in your data source? Are you configuring it properly? That's the part of the code (or configuration) that we're not seeing.

Also, print a stack trace or something, as the above user said, so that we know whether an exception is being thrown. And it would be nice to know whether Statement's execute method returns true or false.