Purpose Functions, Methods, Flags, and Values

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Purpose Functions, Methods, Flags, and Values

The following table describes the possible settings for the sysams columns that contain purpose functions or methods, flags, and values. The entries appear in the same order as the corresponding sysams columns.

Keyword	Explanation	Category	Default
am_sptype	A character that specifies from what type of storage space a primary or secondary-access method can access data. The am_sptype character can have any of the following settings: 'X' indicates the method accesses only extspaces. 'S ' indicates the method accesses only sbspaces. 'A' indicates the method can access extspaces and sbspaces. Valid only for a new access method. You cannot change or add an am_sptype value with ALTER ACCESS_METHOD. Do not set am_sptype to 'D' or attempt to store a virtual table in a dbspace.	Value	Virtual-Table Interface (C): 'A'
am_defopclass	The default operator class for a secondary-access method. The access method must exist before you can define its operator class, so you set this value in the ALTER ACCESS_METHOD statement.	Value	None
am_keyscan	A flag that, if set, indicates that am_getnext returns rows of index keys for a secondary-access method. If a query selects only the columns in the index key, the database server uses the row of index keys that the secondary-access method puts in shared memory, without reading the table.	Flag	Not set
am_unique	A flag to set if a secondary-access method checks for unique keys	Flag	Not set
am_cluster	A flag that you set if a primary- or secondary-access method supports clustering of tables	Flag	Not set
am_rowids	A flag that you set if a primary-access method can retrieve a row from a specified address	Flag	Not set
am_readwrite	A flag to set if a primary-access method supports data changes. The default setting, not set, indicates that the virtual data is read-only. For the C Virtual-Table Interface, set this flag if your application will write data, to avoid the following problems: An INSERT, DELETE, UPDATE, or ALTER FRAGMENT statement causes an SQL error. Function am_insert, am_delete, or am_update is not executed.	Flag	Not set
am_parallel	A flag that the database server sets to indicate which purpose functions or methods can execute in parallel in a primary or secondary-access method. If set, the hexadecimal am_parallel bitmap contains one or more of the following bit settings: The `1` bit is set for parallelizable scan. The `2` bit is set for parallelizable delete. The `4` bit is set for parallelizable update. The `8` bit is set for parallelizable insert. Insertions, deletions, and updates are not supported in the Java Virtual-Table Interface.	Flag	Not set
am_costfactor	A value by which the database server multiplies the cost that the am_scancost purpose function or method returns for a primary or secondary-access method. An am_costfactor value from 0.1 to 0.9 reduces the cost to a fraction of the value that am_scancost calculates. An am_costfactor value of 1.1 or greater increases the am_scancost value.	Value	1.0
am_create	A keyword that you associate with a user-defined function or method (UDR) name that creates a virtual table or virtual index	Task	None
am_drop	A keyword that you associate with the name of a UDR that drops a virtual table or virtual index	Task	None
am_open	A keyword that you associate with the name of a UDR that makes a fragment, extspace, or sbspace available	Task	None
am_close	A keyword that you associate with the name of a UDR that reverses the initialization that am_open performs	Task	None
am_insert	A keyword that you associate with the name of a UDR that inserts a row or an index entry	Task	None
am_delete	A keyword that you associate with the name of a UDR that deletes a row or an index entry	Task	None
am_update	A keyword that you associate with the name of a UDR that changes the values in a row or key	Task	None
am_stats	A keyword that you associate with the name of a UDR that builds statistics based on the distribution of values in storage spaces	Task	None
am_scancost	A keyword that you associate with the name of a UDR that calculates the cost of qualifying and retrieving data	Task	None
am_check	A keyword that you associate with the name of a UDR that tests the physical structure of a table or performs an integrity check on an index	Task	None
am_beginscan	A keyword that you associate with the name of a UDR that sets up a scan	Task	None
am_endscan	A keyword that you associate with the name of a UDR that reverses the setup that am_beginscan initializes	Task	None
am_rescan	A keyword that you associate with the name of a UDR that scans for the next item from a previous scan to complete a join or subquery	Task	None
am_getnext	A keyword that you associate with the name of the required UDR that scans for the next item that satisfies a query	Task	None
am_getbyid	A keyword that you associate with the name of a UDR that fetches data from a specific physical address; am_getbyid is available only for primary-access methods	Task	None
am_truncate	A keyword that you associate with the name of a UDR that deletes all rows of a virtual table (primary-access method) or that deletes all corresponding keys in a virtual index (secondary-access method)	Task	None

The following rules apply to the purpose-option specifications in the CREATE ACCESS_METHOD and ALTER ACCESS_METHOD statements:

To specify multiple purpose options in one statement, separate them with commas.
The CREATE ACCESS_METHOD statement must specify a user-defined function or method name that corresponds to the am_getnext keyword.
The ALTER ACCESS_METHOD statement cannot drop the function or method name that corresponds to am_getnext but can modify it.
The ALTER ACCESS_METHOD statement cannot add, drop, or modify the am_sptype value.
You can specify the am_defopclass value only with the ALTER ACCESS_METHOD statement.
You must first register a secondary-access method with the CREATE ACCESS_METHOD statement before you can assign a default operator class.