Class SpaceTable

java.lang.Object
org.apache.derby.vti.VTITemplate
org.apache.derby.diag.SpaceTable
All Implemented Interfaces:
AutoCloseable, ResultSet, Wrapper, AwareVTI, VTICosting
public class SpaceTable extends VTITemplate implements VTICosting
SpaceTable is a virtual table that shows the space usage of a particular table and its indexes. This virtual table can be invoked by calling it directly, and supplying the schema name and table name as arguments. 
 SELECT * FROM TABLE(SYSCS_DIAG.SPACE_TABLE('MYSCHEMA', 'MYTABLE')) T;
If the schema name is not supplied, the default schema is used. 
 SELECT * FROM TABLE(SYSCS_DIAG.SPACE_TABLE('MYTABLE')) T;

NOTE: Both the schema name and the table name must be any expression that evaluates to a string data type. If you created a schema or table name as a non-delimited identifier, you must present their names in all upper case.

The SpaceTable virtual table can be used to estimate whether space might be saved by compressing a table and its indexes.

The SpaceTable virtual table has the following columns:

  • CONGLOMERATENAME varchar(128) - nullable. The name of the conglomerate, which is either the table name or the index name. (Unlike the SYSCONGLOMERATES column of the same name, table ID's do not appear here).
  • ISINDEX SMALLINT - not nullable. Is not zero if the conglomerate is an index, 0 otherwise.
  • NUMALLOCATEDPAGES bigint - not nullable. The number of pages actively linked into the table. The total number of pages in the file is the sum of NUMALLOCATEDPAGES + NUMFREEPAGES.
  • NUMFREEPAGES bigint - not nullable. The number of free pages that belong to the table. When a new page is to be linked into the table the system will move a page from the NUMFREEPAGES list to the NUMALLOCATEDPAGES list. The total number of pages in the file is the sum of NUMALLOCATEDPAGES + NUMFREEPAGES.
  • NUMUNFILLEDPAGES bigint - not nullable. The number of unfilled pages that belong to the table. Unfilled pages are allocated pages that are not completely full. Note that the number of unfilled pages is an estimate and is not exact. Running the same query twice can give different results on this column.
  • PAGESIZE integer - not nullable. The size of the page in bytes for that conglomerate.
  • ESTIMSPACESAVING bigint - not nullable. The estimated space which could possibly be saved by compressing the conglomerate, in bytes.
  • TABLEID char(36) - not nullable. The UUID of the table.

To get space information on all schemas and tables, use a query such as 

   select v.*
   from SYS.SYSSCHEMAS s,
        SYS.SYSTABLES t,
        TABLE(SYSCS_DIAG.SPACE_TABLE(SCHEMANAME, TABLENAME)) v
   where s.SCHEMAID = t.SCHEMAID;