CURSOR-BUFFER

This statement sets the size of the cursor buffer.

Definition

A lower-level DBH option of STORAGE-SIZE

Function

Cursor files are DBH-specific work files that are available for processing retrieval statements. The DBH stores intermediate results of retrieval statements in them. Access to internal cursor files is via the cursor buffer, provided it is large enough.

You can use the DBH option CURSOR-BUFFER to set the size of the cursor buffer so as to minimize the number of accesses to internal cursor files. You specify the size of the cursor buffer in units of 1 Kbyte.

You can adjust the values of the operands during the DBH session by means of the RECONFIGURE-DBH-SESSION administration statement (see "RECONFIGURE-DBH-SESSION").

CURSOR-BUFFER

= *STD / *PARAMETERS(...)
	*PARAMETERS(...)
		|	BUFFER-SIZE = *STD / <integer 72..1500000>
		|	,FRAME-SIZE = 4 / <integer 4..32>

Operands

CURSOR-BUFFER = *STD

The default values for the size of the cursor buffer are described under *PARAMETERS(...).

CURSOR-BUFFER = *PARAMETERS(...)
Modifies the cursor buffer settings.

BUFFER-SIZE = *STD / <integer 72..1500000>
Sets the size of the cursor buffer in units of 1 Kbyte.
The default value of CURSOR-BUFFER depends on the maximum permitted number of concurrent active threads that you specify using the DBH option THREADS and the number of system threads required. A minimum of 32 Kbytes is required per thread. If you specify a value for BUFFER-SIZE that is smaller than the product of the minimum size per thread and the number of threads (THREADS option plus the number of system threads), then it is rounded up to the minimum size.

FRAME-SIZE = 4 / <integer 4..32>

Sets the size of the cursor buffer frame in units of 1 Kbyte. The default value is 4. Other valid specifications in the range of <integer 4..32> are always rounded off to a number that is a multiple of 4.

The minimum size of CURSOR-BUFFER per thread is dependent on the value of FRAME-SIZE and must in all cases be eight times the value of FRAME-SIZE. If more is specified by the user, the user specifications apply. However, these are always rounded up to a multiple of the FRAME-SIZE value.

Information on cursor files

The operational statistics of the SESAM/SQL utility SESMON provide useful information on cursor files.
The “SYSTEM INFORMATION” form displays the number of cursor files that are currently open (see "DBH form SYSTEM INFORMATION").
The cursor buffer should be large enough to keep to a minimum the number of times internal cursor files are accessed. The “I/O” form (see "DBH form I/O") helps you set the optimum size for the cursor buffer. It displays the number of logical and physical accesses of the cursor files.

The “ Performance” manual describes the cases in which it is advisable to modify the size of the cursor buffer the next time the DBH starts up.