Table of Contents
Database catalogs opened with the file: protocol are stored as a set of files. This document describes the contents of these files and how they are stored.
A database named 'test' is used in this description. The database files will be as follows.
Database Files
| test.properties | Contains the entry 'modified'. If the entry 'modified' is set to 'yes' then the database is either running or was not closed correctly. When the database is properly shutdown, 'modified' is set to 'no'. You can add the optional entry readonly=true to make the database files read only. | 
| test.script | This file contains the SQL statements that makes up the database up to the last checkpoint. All the data for MEMORY tables is also stored in this file. | 
| test.data | This file contains the binary data records for CACHED tables only. | 
| test.backup | This file contains a backup of the parts of the
           | 
| test.log | This file contains the extra SQL statements that have modified the database since the last checkpoint. It is used as a redo log. | 
| test.lobs | This file contains the lobs. If a database has no BLOB or CLOB object, this file will not be present. This file contains all the lobs that are currently in the database, as well as those that belong to rows that have been deleted since the last checkpoint. The space for deleted lobs is always reused after a CHECKPOINT. | 
A CHECKPOINT is an operations that saves all the changed data and
    removes the test.log followed by the creation of an
    empty log. It also deletes the test.backup file. A
    SHUTDOWN is equivalent to a CHECKPOINT followed by closing the
    database.
The disk space needed for the database depends on the amount of
    data. After the database is opened more space, up to slightly greater than
    the size of the test.script and
    test.data files is needed during operation.
Database is closed correctly
State after running the SHUTDOWN
      statement
The test.data file is fully updated.
There is no test.backup file.
The test.script contains all the metadata
        and CREATE TABLE and other DDL statements. It also contains the data
        for MEMORY tables.
The test.properties contains the entry
        'modified' set to 'no'.
There is no test.log file.
Database is closed correctly with SHUTDOWN SCRIPT
State after running the SHUTDOWN SCRIPT
      statement
The test.data file does not exist; all
        CACHED table data is now in the test.script
        file
There is no test.backup file.
The test.script contains all the metadata
        and DDL statements, followed by the data for MEMORY, CACHED and TEXT
        tables.
The test.properties contains the entry
        'modified' set to 'no'.
There is no test.log file.
Database is aborted
If the database process was terminated without a SHUTDOWN, or the SHUTDOWN IMMEDIATELY command was used, the database is in aborted state.
Aborted database state
The test.properties contains
        'modified=yes'.
The test.script contains a snapshot of the
        database at the last checkpoint.
The test.data file is not necessarily
        consistent.
The test.backup file contains just sections
        of the original test.data file that correspond to
        test.script at the time of the last
        checkpoint.
The test.log file contain all data change
        statements executed since the last checkpoint. As a result of abnormal
        termination, the end of file may be incomplete.
The database engine performs the following procedures internally in different circumstances.
Procedure B.1. Clean HyperSQL database shutdown
The test.data file is written completely
          (all the modified cached table rows are written out) and
          closed.
The file test.script.new is created using
          the current state of the database.
The entry 'modified' in the properties file is set to
          'yes-new-files' (Note: after this step, the
          test.data and
          test.script.new files constitute the
          database)
The file test.log is deleted
The file test.script is deleted
The file test.script.new is renamed to
          test.script
The file test.backup is deleted
The entry 'modified' in the properties file is set to 'no'
Procedure B.2. Opening the Database
Check if the database files are in use by checking a special
          test.lck file.
See if the test.properties file exists,
          otherwise create it.
If the test.script did not exist, then
          this is a new database.
If it is an existing database, check in the
          test.properties file if 'modified=yes'. In this
          case the RESTORE operation is performed before the database is
          opened normally.
Otherwise, if in the test.properties file
          'modified=yes-new-files', then the (old)
          test.backup and
          test.script files are deleted if they exist and
          the new test.script.new file is renamed to
          test.script.
Open the test.script file and create the
          database objects.
Create the empty test.log to append any
          data change statements.
The current test.data file is not necessarily
      consistent. The database engine takes these steps:
Procedure B.3. Restore a Database
Restore the old test.data file from the
          backup by copying the original sections from the
          test.backup file.
Execute all the statements in the
          test.script file.
Execute all statements in the test.log
          file. If due to incomplete statements in this file an exception is
          thrown, the rest of the lines in the test.log
          file are ignored. This can be overridden with the database
          connection property hsqldb.full_log_replay=true
          which results in the startup process to fail and allows the user to
          examine and edit the test.log file.
Close the database files.
Open the restored database.
$Revision: 6787 $