SYSCS_UTIL.SYSCS_INPLACE_COMPRESS_TABLE system procedure

Typically, unused allocated space exists when a large amount of data is deleted from a table and there have not been any subsequent inserts to use the space created by the deletes. By default, Derby does not return unused space to the operating system. For example, once a page has been allocated to a table or index, it is not automatically returned to the operating system until the table or index is destroyed. SYSCS_UTIL.SYSCS_INPLACE_COMPRESS_TABLE allows you to return unused space to the operating system.

This system procedure can be used to force three levels of in-place compression of a SQL table: PURGE_ROWS, DEFRAGMENT_ROWS, and TRUNCATE_END. Unlike SYSCS_UTIL.SYSCS_COMPRESS_TABLE, all work is done in place in the existing table/index.

Syntax

SYSCS_UTIL.SYSCS_INPLACE_COMPRESS_TABLE(
		IN SCHEMANAME VARCHAR(128),
		IN TABLENAME VARCHAR(128),
		IN PURGE_ROWS SMALLINT,
		IN DEFRAGMENT_ROWS SMALLINT,
		IN TRUNCATE_END SMALLINT )

SCHEMANAME

An input argument of type VARCHAR(128) that specifies the schema of the table. Passing a null will result in an error.

TABLENAME

An input argument of type VARCHAR(128) that specifies the table name of the table. The string must exactly match the case of the table name, and the argument of "Fred" will be passed to SQL as the delimited identifier 'Fred'. Passing a null will result in an error.

PURGE_ROWS

If PURGE_ROWS is set to a non-zero value, then a single pass is made through the table which will purge committed deleted rows from the table. This space is then available for future inserted rows, but remains allocated to the table. As this option scans every page of the table, its performance is linearly related to the size of the table.

DEFRAGMENT_ROWS

If DEFRAGMENT_ROWS is set to a non-zero value, then a single defragment pass is made which will move existing rows from the end of the table towards the front of the table. The goal of defragmentation is to empty a set of pages at the end of the table which can then be returned to the operating system by the TRUNCATE_END option. It is recommended to only run DEFRAGMENT_ROWS if also specifying the TRUNCATE_END option. The DEFRAGMENT_ROWS option scans the whole table and needs to update index entries for every base table row move, so the execution time is linearly related to the size of the table.

TRUNCATE_END

If TRUNCATE_END is set to a non-zero value, then all contiguous pages at the end of the table will be returned to the operating system. Running the PURGE_ROWS and/or DEFRAGMENT_ROWS options may increase the number of pages affected. This option by itself performs no scans of the table.

Execute privileges

If authentication and SQL authorization are both enabled, all users have execute privileges on this procedure. However, in order for the procedure to run successfully on a given table, the user must be the owner of either the database or the schema in which the table resides. See "Enabling user authentication" and "Setting the SQL standard authorization mode" in the Derby Developer's Guide for more information.

SQL example

call SYSCS_UTIL.SYSCS_INPLACE_COMPRESS_TABLE('US', 'CUSTOMER', 1, 1, 1);

call SYSCS_UTIL.SYSCS_INPLACE_COMPRESS_TABLE('US', 'CUSTOMER', 0, 0, 1);

Java example

CallableStatement cs = conn.prepareCall
("CALL SYSCS_UTIL.SYSCS_INPLACE_COMPRESS_TABLE(?, ?, ?, ?, ?)");
cs.setString(1, "US");
cs.setString(2, "CUSTOMER");
cs.setShort(3, (short) 1);
cs.setShort(4, (short) 1);
cs.setShort(5, (short) 1);
cs.execute();

CallableStatement cs = conn.prepareCall
("CALL SYSCS_UTIL.SYSCS_INPLACE_COMPRESS_TABLE(?, ?, ?, ?, ?)");
cs.setString(1, "US");
cs.setString(2, "CUSTOMER");
cs.setShort(3, (short) 0);
cs.setShort(4, (short) 0);
cs.setShort(5, (short) 1);
cs.execute();