Appendix C. Hsqldb Database Files and RecoveryAppendix C. Hsqldb Database Files and Recovery   Appendix C. Hsqldb Database Files and Recovery
This text is based on HypersonicSQL documentation, updated to reflect
the latest version 1.8.0 of HSQLDB.
$Date: 2005/07/01 17:06:32 $Table of ContentsStatesProceduresClean ShutdownStartupRepair
The Standalone and Client/Server modes will in most cases use files to
store all data to disk in a persistent and safe way.
This document describes the meaning of the files, the states and the
procedures followed by the engine to recover the data.

A database named 'test' is used in this description.
The database files will be as follows.
Database Filestest.properties
Contains the entry 'modified'.
If the entry 'modified' is set to 'yes' then the database is either
running or was not closed correctly (because the close algorithm sets
'modified' to 'no' at the end).
test.script
This file contains the SQL statements that makes up the database up to
the last checkpoint - it is in synch with
test.backup.
test.data
This file contains the (binary) data records for CACHED tables only.
test.backup
This is compressed file that contains the complete backup of the old
test.data file at the time of last checkpoint.
test.log
This file contains the extra SQL statements that have modified the
database since the last checkpoint (something like the 'Redo-log' or
'Transaction-log', but just text).

In the above list, a checkpoint results from both a CHECKPOINT command
and a SHUTDOWN command.
StatesDatabase is closed correctlyState after using the command SHUTDOWN
The test.data file is fully updated.

The test.backup contains the compressed
test.data file.

The test.script contains the information in
the database, excluding data for CACHED and TEXT tables.

The test.properties contains the entry
'modified' set to 'no'.

There is no test.log file.
Database is closed correctly with SHUTDOWN SCRIPTState after using the command SHUTDOWN SCRIPT
The test.data file does not exist; all CACHED
table data is in the test.script file

The test.backup does not exist.

The test.script contains the information in
the database, including data for CACHED and TEXT tables.

The test.properties contains the entry
'modified' set to 'no'.

There is no test.log file.
Database is aborted
This may happen by sudden power off, Ctrl+C in Windows, but may be
simulated using the command SHUTDOWN IMMEDIATELY.
Aborted Database state
The test.properties still containes
'modified=yes'.

The test.script contains a snapshot of the
database at the last checkpoint and is OK.

The test.data file may be corrupt because the
cache in memory was not written out completely.

The test.backup file contains a snapshot of
test.data that corresponds to
test.script.

The test.log file contain all information to
re-do all changes since the snanapshot.
As a result of abnormal termination, this file may be partially
corrupt.
Procedures
The database engine performs the following procedures internally in
different circumstances.
Clean ShutdownProcedure C.1. Clean Hsqldb database shutdown
The test.data file is written completely
(all the modified cached table rows are witten out) and closed.

The test.backup.new is created (containing
the compressed test.data file)

The file test.script.new is created using
the information in the database (and thus shrinks because no
UPDATE and DELETE statements; only INSERT).

The entry 'modified' in the properties file is set to
'yes-new-files'

The file test.script is deleted

The file test.script.new is renamed to
test.script

The file test.backup is deleted

The file test.backup.new is renamed to
test.backup

The entry 'modified' in the properties file is set to 'no'

The file test.log is deleted
StartupProcedure C.2. Database is opened
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.properties did not exist, then
this is a new database.
Create the empty test.log to append new
commands.

If it is an existing database, check in the
test.properties file if 'modified=yes'.
This would mean last time it was not closed correctly, and thus
the test.data file may be corrupted or
incomplete.
In this case the 'REPAIR' algorithm is executed (see below),
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 and the new
test.script.new file is renamed to
test.script.

Open the test.script file and execute the
commands.

Create the empty test.log to append new commands.
Repair
The current test.data file is corrupt, but
with the old test.data (from the
test.backup file and
test.script) and the current
test.log, the database is made up-to-date.
The database engine takes these steps:
Procedure C.3. Database Repair
Restore the old test.data file from
the backup (uncompress the test.backup
and overwrite test.data).

Execute all commands in the test.script
file.

Execute all commands in the test.log file.
If due to corruption, an exception is thrown, the rest of the
lines of command in the test.log file are
ignored.

Close the database correctly (including a backup).
  Appendix B. First JDBC Client Example  Appendix D. Running Hsqldb with OpenOffice.org 1.1.x