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: 6752 $