HSQLDB example source code file (running.xml)

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The HSQLDB running.xml source code

<?xml version="1.0" encoding="UTF-8"?>
<!-- $Id: running.xml,v 1.21 2005/09/19 00:03:12 unsaved Exp $ -->
<chapter>
  <title>Running and Using Hsqldb

  <chapterinfo>
    <authorgroup>
      <author>
        <firstname>Fred

        <surname>Toussi

        <affiliation>
          <orgname>HSQLDB Development Group
        </affiliation>

        <email>ft@cluedup.com
      </author>
    </authorgroup>

    <edition>$Revision: 1.21 $

    <pubdate>$Date: 2005/09/19 00:03:12 $

    <keywordset>
      <keyword>Hsqldb

      <keyword>Guide
    </keywordset>

    <legalnotice>
      <para>Copyright 2002-2005 Fred Toussi. Permission is granted to
      distribute this document without any alteration under the terms of the
      HSQLDB license. Additional permission is granted to the HSQLDB
      Development Group to distribute this document with or without
      alterations under the terms of the HSQLDB license.</para>
    </legalnotice>
  </chapterinfo>

  <section>
    <title>Introduction

    <para>The HSQLDB jar package is located in the /lib directory and contains
    several components and programs. Different commands are used to run each
    program.</para>

    <itemizedlist>
      <title>Components of the Hsqldb jar package

      <listitem>
        <para>HSQLDB RDBMS
      </listitem>

      <listitem>
        <para>HSQLDB JDBC Driver
      </listitem>

      <listitem>
        <para>Database Manager (Swing and AWT versions)
      </listitem>

      <listitem>
        <para>Query Tool (AWT)
      </listitem>

      <listitem>
        <para>Sql Tool (command line)
      </listitem>
    </itemizedlist>

    <para>The HSQLDB RDBMS and JDBC Driver provide the core functionality. The
    rest are general-purpose database tools that can be used with any database
    engine that has a JDBC driver.</para>
  </section>

  <section>
    <title>Running Tools

    <para>All tools can be run in the standard way for archived Java classes.
    In the following example the AWT version of the Database Manager, the
    <filename>hsqldb.jar is located in the directory
    <filename>../lib relative to the current directory.

    <screen>
    java -cp ../lib/hsqldb.jar org.hsqldb.util.DatabaseManager</screen>

    <para>If hsqldb.jar is in the current directory, the
    command would change to:</para>

    <screen>
    java -cp hsqldb.jar org.hsqldb.util.DatabaseManager</screen>

    <itemizedlist>
      <title>Main classes for the Hsqldb tools

      <listitem>
        <para>
          <classname>org.hsqldb.util.DatabaseManager
        </para>
      </listitem>

      <listitem>
        <para>
          <classname>org.hsqldb.util.DatabaseManagerSwing
        </para>
      </listitem>

      <listitem>
        <para>
          <classname>org.hsqldb.util.Transfer
        </para>
      </listitem>

      <listitem>
        <para>
          <classname>org.hsqldb.util.QueryTool
        </para>
      </listitem>

      <listitem>
        <para>
          <classname>org.hsqldb.util.SqlTool
        </para>
      </listitem>
    </itemizedlist>

    <para>Some tools, such as the Database Manager or SQL Tool, can use
    command line arguments or entirely rely on them. You can add the command
    line argument -? to get a list of available arguments for these tools.
    Database Manager features a graphical user interface and
    can be explored interactively.</para>
  </section>

  <section>
    <title>Running Hsqldb

    <para>HSQLDB can be run in a number of different ways. In general these
    are divided into Server Modes and In-Process Mode (also called Standalone
    Mode). A different sub-program from the jar is used to run HSQLDB in each
    mode.</para>

    <para>Each HSQLDB database consists of between 2 to 5 files, all named the
    same but with different extensions, located in the same directory. For
    example, the database named "test" consists of the following files:</para>

    <itemizedlist>
      <listitem>
        <para>
          <filename>test.properties
        </para>
      </listitem>

      <listitem>
        <para>
          <filename>test.script
        </para>
      </listitem>

      <listitem>
        <para>
          <filename>test.log
        </para>
      </listitem>

      <listitem>
        <para>
          <filename>test.data
        </para>
      </listitem>

      <listitem>
        <para>
          <filename>test.backup
        </para>
      </listitem>
    </itemizedlist>

    <para>The properties files contains general settings about the database.
    The script file contains the definition of tables and other database
    objects, plus the data for non-cached tables. The log file contains recent
    changes to the database. The data file contains the data for cached tables
    and the backup file is a zipped backup of the last known consistent state
    of the data file. All these files are essential and should never be
    deleted. If the database has no cached tables, the
    <filename>test.data and test.backup files
    will not be present. In addition to those files, HSQLDB database may link
    to any formatted text files, such as CSV lists, anywhere on the
    disk.</para>

    <para>While the "test" database is operational, a
    <filename>test.log file is used to write the changes made to
    data. This file is removed at a normal SHUTDOWN. Otherwise (with abnormal
    shutdown) this file is used at the next startup to redo the changes. A
    <filename>test.lck file is also used to record the fact that
    the database is open. This is deleted at a normal SHUTDOWN. In some
    circumstances, a <filename>test.data.old is created and deleted
    afterwards.</para>

    <note>
      <para>When the engine closes the database at a shutdown, it creates
      temporary files with the extension <literal>.new which it then
      renames to those listed above.</para>
    </note>
  </section>

  <section>
    <title>Server Modes

    <para>Server modes provide the maximum accessibility. The database engine
    runs in a JVM and listens for connections from programs on the same
    computer or other computers on the network. Several different programs can
    connect to the server and retrieve or update information. Applications
    programs (clients) connect to the server using the HSQLDB JDBC driver. In
    most server modes, the server can serve up to 10 databases that are
    specified at the time of running the server.</para>

    <para>Server modes can use preset properties or command line arguments as
    detailed in the <link endterm="advanced-title"
    linkend="advanced-chapter" /> chapter. There are three server modes, based
    on the protocol used for communications between the client and
    server.</para>

    <section>
      <title>Hsqldb Server

      <para>This is the preferred way of running a database server and the
      fastest one. A proprietary communications protocol is used for this
      mode. A command similar to those used for running tools and described
      above is used for running the server. The following example of the
      command for starting the server starts the server with one (default)
      database with files named "mydb.*".</para>

      <informalexample>
        <screen>
    java -cp ../lib/hsqldb.jar org.hsqldb.Server -database.0 file:mydb -dbname.0 xdb</screen>
      </informalexample>

      <para>The command line argument -? can be used to get
      a list of available arguments.</para>
    </section>

    <section>
      <title>Hsqldb Web Server

      <para>This mode is used when access to the computer hosting the database
      server is restricted to the HTTP protocol. The only reason for using the
      Web Server mode is restrictions imposed by firewalls on the client or
      server machines and it should not be used where there are no such
      restrictions. The HSQLDB Web Server is a special web server that allows
      JDBC clients to connect via HTTP. From 1.7.2 this mode also supports
      transactions.</para>

      <para>To run a web server, replace the main class for the server in the
      example command line above with the following:</para>

      <informalexample>
        <screen>
    org.hsqldb.WebServer</screen>
      </informalexample>

      <para>The command line argument -? can be used to get
      a list of available arguments.</para>
    </section>

    <section>
      <title>Hsqldb Servlet

      <para>This uses the same protocol as the Web Server. It is used when a
      separate servlet engine (or application server) such as Tomcat or Resin
      provides access to the database. The Servlet Mode cannot be started
      independently from the servlet engine. The
      <filename>Servlet class, in the HSQLDB jar, should be
      installed on the application server to provide the connection. The
      database is specified using an application server property. Refer to the
      source file <filename>org.hsqldb.Servlet.java to see the
      details.</para>

      <para>Both Web Server and Servlet modes can only be accessed using the
      JDBC driver at the client end. They do not provide a web front end to
      the database. The Servlet mode can serve only a single database.</para>

      <para>Please note that you do not normally use this mode if you are
      using the database engine in an application server.</para>

      <section>
        <title>Connecting to a Database running as a Server

        <para>Once an HSQLDB server is running, client programs can connect to
        it using the HSQLDB JDBC Driver contained in
        <filename>hsqldb.jar. Full information on how to connect to
        a server is provided in the Java Documentation for <ulink
            url="../src/org/hsqldb/jdbc/jdbcConnection.html">
            <classname>jdbcConnection
          </ulink> (located in the /doc/src directory of
        HSQLDB distribution. A common example is connection to the default
        port (9001) used for the hsql protocol on the same machine:</para>

        <example>
          <title>Java code to connect to the local Server above

          <programlisting>
    try {
        Class.forName("org.hsqldb.jdbcDriver" );
    } catch (Exception e) {
        System.out.println("ERROR: failed to load HSQLDB JDBC driver.");
        e.printStackTrace();
        return;
    }

    Connection c = DriverManager.getConnection("jdbc:hsqldb:hsql://localhost/xdb", "sa", "");</programlisting>
        </example>

        <para>In some circumstances, you may have to use the following line to
        get the driver.</para>

        <informalexample>
          <programlisting>
    Class.forName("org.hsqldb.jdbcDriver").newInstance();</programlisting>
        </informalexample>

        <para>Note in the above connection URL, there is no mention of the
        database file, as this was specified when running the server. Instead,
        the value defined for dbname.0 is used. Also, see the <link
        endterm="advanced-title" linkend="advanced-chapter" /> chapter for the
        connection URL when there is more than one database per server
        instance.</para>
      </section>

      <section>
        <title>Security Considerations

        <para>When HSQLDB is run as a server, network access should be
        adequately protected. Source IP addresses may be restricted by use of
        TCP filtering or firewall programs, or standalone firewalls. If the
        traffic will cross an unprotected network (such as the Internet), the
        stream should be encrypted (for example by VPN, ssh tunneling, or
        <link endterm="tls-title" linkend="tls-chapter" /> using the SSL
        enabled HSQLS and HTTPS variants of the server and web server modes).
        Only secure passwords should be used-- most importantly, the password
        for the default system user should be changed from the default empty
        string. If you are purposefully providing data to the public, then the
        wide-open public network connection should be used exclusively to
        access the public data via read-only accounts. (I.e., neither secure
        data nor privileged accounts should use this connection). These
        considerations also apply to HSQLDB servers run with the HTTP
        protocol.</para>
      </section>
    </section>

    <section>
      <title>In-Process (Standalone) Mode

      <para>This mode runs the database engine as part of your application
      program in the same Java Virtual Machine. For most applications this
      mode can be faster, as the data is not converted and sent over the
      network. The main drawback is that it is not possible by default to
      connect to the database from outside your application. As a result you
      cannot check the contents of the database with external tools such as
      Database Manager while your application is running. In 1.8.0, you can
      run a server instance in a thread from the same virtual machine as your
      application and provide external access to your in-process
      database.</para>

      <para>The recommended way of using the in-process mode in an application
      is to use an HSQLDB Server instance for the database while developing
      the application and then switch to In-Process mode for
      deployment.</para>

      <para>An In-Process Mode database is started from JDBC, with the
      database file path specified in the connection URL. For example, if the
      database name is testdb and its files are located in the same directory
      as where the command to run your application was issued, the following
      code is used for the connection:</para>

      <programlisting>
    Connection c = DriverManager.getConnection("jdbc:hsqldb:file:testdb", "sa", "");</programlisting>

      <para>The database file path format can be specified using forward
      slashes in Windows hosts as well as Linux hosts. So relative paths or
      paths that refer to the same directory on the same drive can be
      identical. For example if your database path in Linux is
      <filename>/opt/db/testdb and you create an identical
      directory structure on the <literal>C: drive of a Windows
      host, you can use the same URL in both Windows and Linux:</para>

      <programlisting>
    Connection c = DriverManager.getConnection("jdbc:hsqldb:file:/opt/db/testdb", "sa", "");</programlisting>

      <para>When using relative paths, these paths will be taken relative to
      the directory in which the shell command to start the Java Virtual
      Machine was executed. Refer to Javadoc for <ulink
          url="../src/org/hsqldb/jdbc/jdbcConnection.html">
          <classname>jdbcConnection
        </ulink> for more details.
    </section>

    <section>
      <title>Memory-Only Databases

      <para>It is possible to run HSQLDB in a way that the database is not
      persistent and exists entirely in random access memory. As no
      information is written to disk, this mode should be used only for
      internal processing of application data, in applets or certain special
      applications. This mode is specified by the mem: protocol.</para>

      <programlisting>
    Connection c = DriverManager.getConnection("jdbc:hsqldb:mem:aname", "sa", "");</programlisting>

      <para>You can also run a memory-only server instance by specifying the
      same URL in the <filename>server.properties. This usage is
      not common and is limited to special applications where the database
      server is used only for exchanging information between clients, or for
      non-persistent data.</para>
    </section>
  </section>

  <section>
    <title>General

    <section>
      <title>Closing the Database

      <para>All databases running in different modes can be closed with the
      SHUTDOWN command, issued as an SQL query. From version 1.7.2, in-process
      databases are no longer closed when the last connection to the database
      is explicitly closed via JDBC, a SHUTDOWN is required. In 1.8.0, a
      connection property, shutdown=true, can be specified on the first
      connection to the database (the connection that opens the database) to
      force a shutdown when the last connection closes.</para>

      <para>When SHUTDOWN is issued, all active transactions are rolled back.
      A special form of closing the database is via the SHUTDOWN COMPACT
      command. This command rewrites the <literal>.data file that
      contains the information stored in CACHED tables and compacts it to
      size. This command should be issued periodically, especially when lots
      of inserts, updates or deletes have been performed on the cached tables.
      Changes to the structure of the database, such as dropping or modifying
      populated CACHED tables or indexes also create large amounts of unused
      file space that can be reclaimed using this command.</para>
    </section>

    <section>
      <title>Using Multiple Databases in One JVM

      <para>In the above examples each server serves only one database and
      only one in-memory database can be created. However, from version 1.7.2,
      HSQLDB can serve several databases in multiple server modes and allow
      simultaneous access to multiple in-process and memory-only databases.
      These capabilities are covered in the <link endterm="advanced-title"
      linkend="advanced-chapter" /> chapter.</para>
    </section>

    <section>
      <title>Creating a New Database

      <para>When a server instance is started, or when a connection is made to
      an in-process database, a new, empty database is created if no database
      exists at the given path.</para>

      <para>This feature has a side effect that can confuse new users. If a
      mistake is made in specifying the path for connecting to an existing
      database, a connection is nevertheless established to a new database.
      For troubleshooting purposes, you can specify a connection property
      <property>ifexists=true to allow
      connection to an existing database only and avoid creating a new
      database. In this case, if the database does not exist, the
      <literal>getConnection() method will throw an
      exception.</para>
    </section>
  </section>

  <section>
    <title>Using the Database Engine

    <para>Once a connection is established to a database in any mode, JDBC
    methods are used to interact with the database. The Javadoc for <ulink
        url="../src/org/hsqldb/jdbc/jdbcConnection.html">
        <classname>jdbcConnection
      </ulink>, 
        <classname>jdbcDriver
      </ulink>, 
        <classname>jdbcDatabaseMetadata
      </ulink>, 
        <classname>jdbcResultSet
      </ulink>, 
        <classname>jdbcStatement
      </ulink>, and 
      </ulink> list all the supported JDBC methods together with information
    that is specific to HSQLDB. JDBC methods are broadly divided into:
    connection related methods, metadata methods and database access methods.
    The database access methods use SQL commands to perform actions on the
    database and return the results either as a Java primitive type or as an
    instance of the <classname>java.sql.ResultSet class.

    <para>You can use Database Manager or other Java database access tools to
    explore your database and update it with SQL commands. These programs use
    JDBC internally to submit your commands to the database engine and to
    display the results in a human readable format.</para>

    <para>The SQL dialect used in HSQLDB is as close to the SQL92 and SQL200n
    standards as it has been possible to achieve so far in a small-footprint
    database engine. The full list of SQL commands is in the <link
    endterm="sqlsyntax-title" linkend="sqlsyntax-chapter" /> chapter.</para>

    <section>
      <title>Different Types of Tables

      <para>HSQLDB supports TEMP tables and three types of persistent
      tables.</para>

      <para>TEMP tables are not written to disk and last only for the lifetime
      of the Connection object. The contents of each TEMP table is visible
      only from the Connection that was used to populate it; other concurrent
      connections to the database will have access to their own copies of the
      table. Since 1.8.0 the definition of TEMP tables conforms to the GLOBAL
      TEMPORARY type in the SQL standard. The definition of the table persists
      but each new connections sees its own copy of the table, which is empty
      at the beginning. When the connection commits, the contents of the table
      are cleared by default. If the table definition statements includes ON
      COMMIT PRESERVE ROWS, then the contents are kept when a commit takes
      place.</para>

      <para>The three types of persistent tables are MEMORY tables, CACHED
      tables and TEXT tables.</para>

      <para>Memory tables are the default type when the CREATE TABLE command
      is used. Their data is held entirely in memory but any change to their
      structure or contents is written to the
      <filename><dbname>.script file. The script file is read
      the next time the database is opened, and the MEMORY tables are
      recreated with all their contents. So unlike TEMP table, the default,
      MEMORY tables are persistent.</para>

      <para>CACHED tables are created with the CREATE CACHED TABLE command.
      Only part of their data or indexes is held in memory, allowing large
      tables that would otherwise take up to several hundred megabytes of
      memory. Another advantage of cached tables is that the database engine
      takes less time to start up when a cached table is used for large
      amounts of data. The disadvantage of cached tables is a reduction in
      speed. Do not use cached tables if your data set is relatively small. In
      an application with some small tables and some large ones, it is better
      to use the default, MEMORY mode for the small tables.</para>

      <para>TEXT tables are supported since version 1.7.0 and use a CSV (Comma
      Separated Value) or other delimited text file as the source of their
      data. You can specify an existing CSV file, such as a dump from another
      database or program, as the source of a TEXT table. Alternatively, you
      can specify an empty file to be filled with data by the database engine.
      TEXT tables are efficient in memory usage as they cache only part of the
      text data and all of the indexes. The Text table data source can always
      be reassigned to a different file if necessary. Two commands are needed
      to set up a TEXT table as detailed in the <link
      endterm="texttables-title" linkend="texttables-chapter" />
      chapter.</para>

      <para>With memory-only databases (see above), both MEMORY table and
      CACHED table declarations are treated as declarations for non-persistent
      memory tables. TEXT table declarations are not allowed in this
      mode.</para>
    </section>

    <section>
      <title>Constraints and Indexes

      <para>HSQLDB supports PRIMARY KEY, NOT NULL, UNIQUE, CHECK and FOREIGN
      KEY constraints. In addition, it supports UNIQUE or ordinary indexes.
      This support is fairly comprehensive and covers multi-column constraints
      and indexes, plus cascading updates and deletes for foreign keys.</para>

      <para>HSQLDB creates indexes internally to support PRIMARY KEY, UNIQUE
      and FOREIGN KEY constraints: a unique index is created for each PRIMARY
      KEY or UNIQUE constraint; an ordinary index is created for each FOREIGN
      KEY constraint. Because of this, you should not create duplicate
      user-defined indexes on the same column sets covered by these
      constraints. This would result in unnecessary memory and speed
      overheads. See the discussion in the <link endterm="sql_issues-title"
      linkend="sql_issues-chapter" /> chapter for more information.</para>

      <para>Indexes are crucial for adequate query speed. When queries joining
      multiple tables are used, there must be an index on each joined column
      of each table. When range or equality conditions are used e.g.
      <literal>SELECT ... WHERE acol >10 AND bcol = 0, an indexe
      is required on the acol column used in the condition. Indexes have no
      effect on ORDER BY clauses or some LIKE conditions.</para>

      <para>As a rule of thumb, HSQLDB is capable of internal processing of
      queries at over 100,000 rows per second. Any query that runs into
      several seconds should be checked and indexes should be added to the
      relevant columns of the tables if necessary.</para>
    </section>

    <section>
      <title>SQL Support

      <para>The SQL syntax supported by HSQLDB is essentially that specified
      by the SQL Standard (92 and 200n). Not all the features of the Standard
      are supported and there are some proprietary extensions. In 1.8.0 the
      behaviour of the engine is far more compliant with the Standards than
      with older versions. The main changes are</para>

      <itemizedlist>
        <listitem>
          <para>correct treatment of NULL column values in joins, in UNIQUE
          constraints and in query conditions</para>
        </listitem>

        <listitem>
          <para>correct processing of selects with JOIN and LEFT OUTER
          JOIN</para>
        </listitem>

        <listitem>
          <para>correct processing of aggregate functions contained in
          expressions or containing expression arguments</para>
        </listitem>
      </itemizedlist>

      <para>The supported commands are listed in the 

      <para>Since 1.7.2, support for JDBC2 has been significantly extended and
      some features of JDBC3 are also supported. The relevant classes are
      thoroughly documented. See the JavaDoc for <ulink
      url="../src/index.html">org.hsqldb.jdbcXXXX </ulink> classes.
    </section>
  </section>
</chapter>