Chapter 12. Properties

This property, when set true, prevents SQL keywords being used for database object names such as columns and tables.

SET DATABASE SQL NAMES { TRUE | FALSE }

This property, when set true, prevents database object names such as columns and tables beginning with the underscore or containing the dollar character.

SET DATABASE SQL REGULAR NAMES { TRUE | FALSE }

This property, when set true, causes an error when an SQL statement (usually a select statement) contains column references that can be resolved by more than one table name or alias. In effect forces such column references to have a table name or table alias qualifier.

SET DATABASE SQL REFERENCES { TRUE | FALSE }

Conforms to SQL standards for size and precision of data types. When true, all VARCHAR column type declarations require a size. When the property is false and there is no size in the declaration, a default size is used. Note that all other types accept a declaration without a size, which is interpreted as a default size.

SET DATABASE SQL SIZE { TRUE | FALSE }

This property, when set true, causes an error when an SQL statements contains comparisons or assignments that are non-standard due to type mismatch. Most illegal comparisons and assignments will cause an exception regardless of this setting. This setting applies to a small number of comparisons and assignments that are possible, but not standard conformant, and were allowed in previous versions of HSQLDB.

SET DATABASE SQL TYPES { TRUE | FALSE }

The ON DELETE and ON UPDATE clauses of constraints cause data changes in rows in different tables or the same table. When there are multiple constraints, a row may be updated by one constraint and deleted by another constraint in the same operation. This is not allowed by default. Changing this property to false allows such violations of the Standard to pass without an exception. Used for porting from database engines that do not enforce the constraints.

SET DATABASE SQL TDC DELETE { TRUE | FALSE }

The ON DELETE and ON UPDATE clauses of foreign key constraints cause data changes in rows in different tables or the same table. With multiple constraint, a field may be updated by two constraints and set to different values. This is not allowed by default. Changing this property to false allows such violations of the Standard to pass without an exception. Used for porting from database engines that do not enforce the constraints properly.

SET DATABASE SQL TDC UPDATE { TRUE | FALSE }

This property, when set true, causes type declarations using LONGVARCHAR and LONGVARBINARY to be translated to CLOB and BLOB respectively. By default, they are translated to VARCHAR and VARBINARY.

SET DATABASE SQL LONGVAR IS LOB { TRUE | FALSE }

This property, when set false, causes the concatenation of a null and a not null value to return the not null value. By default, it returns null.

SET DATABASE SQL CONCAT NULLS { TRUE | FALSE }

This property, when set false, causes multi-column unique constrains to be more restrictive for value sets that contain a mix of null and not null values.

SET DATABASE SQL UNIQUE NULLS { TRUE | FALSE }

This property, when set false, causes type conversions from DOUBLE to any integral type to use rounding. By default truncation is used.

SET DATABASE SQL CONVERT TRUNCATE { TRUE | FALSE }

By default, the result of a division or an AVG or MEDIAN aggregate has the same type and scale as the aggregated value. For INTEGER types, the scale is 0. When this property is set to a value other than the default 0, then the scale is used if it is greater than the scale of the divisor or aggregated value. This property does not affect DOUBLE values. Values between 0 - 10 can be used for this property.

SET DATABASE SQL AVG SCALE <numeric value>

This property, when set false, causes division of DOUBLE values by Zero to return a Double.NaN value. By default an exception is thrown.

SET DATABASE SQL DOUBLE NAN { TRUE | FALSE }

By default, nulls appear before not-null values when a result set is ordered without specifying NULLS FIRST or NULLS LAST. This property, when set false, causes nulls to appear by default after not-null values in result sets with ORDER BY

SET DATABASE SQL NULLS FIRST { TRUE | FALSE }

By default, when two strings are compared, he shorter string is padded with spaces before comparison. When this property is set false, no padding takes place before comparison. Without padding, the shorter string is never equal to the longer one.

Before version 2.0, HSQLDB used NO PAD comparison. If you need the old behaviour, use this property when opening an older database.

SET DEFAULT COLLATION <collation name> [ NO PAD | PAD SPACE ]

This property, when set true, allows compatibility with some aspects of this dialect.

SET DATABASE SQL SYNTAX DB2 { TRUE | FALSE }

This property, when set true, switches the arguments of the CONVERT function and also allow compatibility with some other aspects of this dialect.

SET DATABASE SQL SYNTAX MSS { TRUE | FALSE }

This property, when set true, enables support for TEXT and AUTO_INCREMENT types and also allow compatibility with some other aspects of this dialect.

SET DATABASE SQL SYNTAX MYS { TRUE | FALSE }

This property, when set true, enables support for non-standard types. It also enables DUAL, ROWNUM, NEXTVAL and CURRVAL syntax and and also allow compatibility with some other aspects of this dialect.

SET DATABASE SQL SYNTAX ORA { TRUE | FALSE }

This property, when set true, enables support for TEXT and SERIAL types. It also enables NEXTVAL, CURRVAL and LASTVAL syntax and also allow compatibility with some other aspects of this dialect.

SET DATABASE SQL SYNTAX PGS { TRUE | FALSE }

The CREATE TABLE command results in a MEMORY table by default. Setting the value cached for this property will result in a cached table by default. The qualified forms such as CREATE MEMORY TABLE or CREATE CACHED TABLE are not affected at all by this property.

SET DATABASE DEFAULT TABLE TYPE { CACHED | MEMORY }

Indicates the transaction control mode for the database. The values, locks, mvlocks and mvcc are allowed.

SET DATABASE TRANSACTION CONTROL { LOCKS | MVLOCKS | MVCC }

Indicates the default transaction isolation level for each new session. The values, read_committed and serializable are allowed. Individual sessions can change their isolation level.

SET DATABASE DEFAULT ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE }

When a transaction deadlock or other unresolvable conflict is about to happen, the current transaction is rolled back and an exception is raised. When this property is set false, the transaction is not rolled back. Only the latest action that would cause the conflict is undone and an error is returned. The property should not be changed unless the application can quickly perform an alternative statement and complete the transaction. It is provided for compatibility with other database engines which do not roll back the transaction upon deadlock.

SET DATABASE TRANSACTION ROLLBACK ON CONFLICT { TRUE | FALSE }

If the property is true, the TIME / TIMESTAMP WITH TIME ZONE types and INTERVAL types are represented in JDBC methods of ResultSetMetaData and DatabaseMetaData as JDBC datetime types without time zone and the VARCHAR type respectively. The original type names are preserved.

SET DATABASE SQL TRANSLATE TTI TYPES { TRUE | FALSE }

This property is a special property that can be added manually to the .properties file, or included in the URL or connection properties. When this property is true, the database becomes readonly. This can be used with an existing database to open it for readonly operation.

this property cannot be set with an SQL statement - it can be used in the .properties file

This property is used similarly to the hsqldb.readonly property. When this property is true, CACHED and TEXT tables are readonly but memory tables are not. Any change to the data is not persisted to database files.

this property cannot be set with an SQL statement - it can be used in the .properties file

By default, up to 2 billion rows can be stored in disk-based CACHED tables. Setting this property to true increases the limit to 512 billion rows. This property is used as a connection property.

this property cannot be set with an SQL statement - it can be used as a connection property for the connection that opens the database

This property can be set to specify how many rows of each results or temporary table are stored in memory before the table is written to disk. The default is zero and means data is always stored in memory. If this setting is used, it should be set above 1000.

SET DATABASE DEFAULT RESULT MEMORY ROWS <numeric value>

The default level 0 indicates no logging. Level 1 results in minimal logging, including any failures. Level 2 indicates all events, including ordinary events. LEVEL 3 adds details of some of the normal operations. The events are logged in a file ending with ".app.log".

SET DATABASE EVENT LOG LEVEL { 0 | 1 | 2 | 3}

The default level 0 indicates no logging. Level 1 currently logs only commits and rollbacks. Level 2 currently logs all the SQL statements executed, together with their parameter values. Level 3 will be supported in the future. The events are logged in a file ending with ".sql.log". This property applies to existing file: databases as well as new databases.

SET DATABASE EVENT LOG SQL LEVEL { 0 | 1 | 2 }

The default indicates 512 unused spaces are kept for later use. The value can range between 0 - 8096.

When rows are deleted, the space is recovered and kept for reuse for new rows. If too many rows are deleted, the smaller recovered spaces are lost and the largest ones are retained for later use. Normally there is no need to set this property.

this property cannot be set with an SQL statement

Indicates the maximum number of rows of cached tables that are held in memory.

The value can range between 100- 4 billion. If the value is set via SET FILES then it becomes effective after the next database SHUTDOWN or CHECKPOINT.

SET FILES CACHE ROWS <numeric value>

Indicates the total size (in kilobytes) of rows in the memory cache used with cached tables. This size is calculated as the binary size of the rows, for example an INTEGER is 4 bytes. The actual memory size used by the objects is 2 to 4 times this value. This depends on the types of objects in database rows, for example with binary objects the factor is less than 2, with character strings, the factor is just over 2 and with date and timestamp objects the factor is over 3.

The value can range between 100 KB - 4 GB. The default is 10,000, representing 10,000 kilobytes. If the value is set via SET FILES then it becomes effective after the next database SHUTDOWN or CHECKPOINT.

SET FILES CACHE SIZE <numeric value>

The default value corresponds to a maximum size of 64 GB for the .data file. This can be increased to 64, 128, 256, 512, or 1024 resulting in up to 2 TB GB storage. Settings below 32 in older databases are preserved until a SHUTDOWN COMPACT.

SET FILES SCALE <numeric value>

The default value represents units of 32KB. When the average size of individual lobs in the database is smaller, a smaller unit can be used to reduce the overall size of the .lobs file. Values 1, 2, 4, 8, 16, 32 can be used.

SET FILES LOB SCALE <numeric value>

During updates, the contents of the .data file are modified. When this property is true, the modified contents are backed up gradually. This causes a marginal slowdown in operations, but allows fast checkpoint and shutdown.

When the property is false, the .data file is backed up entirely at the time of checkpoint and shutdown. Up to version 1.8, HSQLDB supported only full backup.

SET FILES BACKUP INCREMENT { TRUE | FALSE }

By default, a lock file is created for each file database that is opened for read and write. This property can be specified with the value false to prevent the lock file from being created. This usage is not recommended but may be desirable when flash type storage is used. This property applies to existing file: databases as well as new databases.

this property cannot be set with an SQL statement

This property can be set to false when database recovery in the event of an unexpected crash is not necessary. A database that is used as a temporary cache is an example. Regardless of the value of this property, if there is a proper shutdown of the database, all the changed data is stored. A checkpoint or shutdown still rewrites the .script file and saves the .backup file according to the other settings.

SET FILES LOG  { TRUE | FALSE }

The value is the size (in megabytes) that the .log file can reach before an automatic checkpoint occurs. A checkpoint rewrites the .script file and clears the .log file.

SET FILES LOG SIZE <numeric value>

When a checkpoint is performed, the percentage of wasted space in the .data file is calculated. If the wasted space is above the specified limit, a defrag operation is performed. The default is 0, which means no automatic checkpoint. The numeric value must be between 0 and 100 and is interpreted as a percentage of the current size of the .data file.

SET FILES DEFRAG <numeric value>

If the property is true, the default WRITE DELAY property of the database is used, which is 500 milliseconds. If the property is false, the WRITE DELAY is set to 0 seconds. The SQL command for this property allows more precise control over the property.

SET FILES WRITE DELAY {{ TRUE | FALSE } | <seconds value> | <milliseconds value> MILLIS

If the property is used, the WRITE DELAY property of the database is set the given value in milliseconds. The SQL command for this property allows the same level of control over the property.

SET FILES WRITE DELAY {{ TRUE | FALSE } | <seconds value> | <milliseconds value> MILLIS

Setting this property to false will avoid the use of nio access methods, resulting in somewhat reduced speed. If the data file is larger than hsqldb.nio_max_size (default 256MB) when it is first opened (or when its size is increased), nio access methods are not used. Also, if the file gets larger than the amount of available computer memory that needs to be allocated for nio access, non-nio access methods are used.

SET FILES NIO { TRUE | FALSE }

The maximum size of .data file in mega bytes that can use the nio access method. When the file gets larger than this limit, non-nio access methods are used. Values 64, 128, 256, 512, 1024, and larger multiples of 512 can be used. The default is 256MB.

SET FILES NIO SIZE <numeric value>

The .log file is processed during recovery after a forced shutdwon. Out of memory conditions always abort the startup. Any other exception stops the processing of the .log file and by default, continues the startup process. If this property is true, the startup process is stopped if any exception occurs. Exceptions are usually caused by incomplete lines of SQL statements near the end of the .log file, which were not fully synced to disk when an abnormal shutdown occurred.

This property cannot be set with an SQL statement

Properties that override the database engine defaults for newly created text tables. Settings in the text table SET <tablename> SOURCE <source string> command override both the engine defaults and the database properties defaults. Individual textdb.* properties are listed in the Text Tables chapter.

This setting forces garbage collection each time a set number of result set row or cache row objects are created. The default, "0" means no garbage collection is forced by the program.

SET DATABASE GC <numeric value>

If the property is true, the contents of the .lobs file is encrypted as well.

this property cannot be set with an SQL statement

The cipher key for an encrypted database.

this property cannot be set with an SQL statement

The fully-qualified class name of the cryptography provider. This property is not used for the default security provider.

this property cannot be set with an SQL statement

The cipher specification.

this property cannot be set with an SQL statement