Provide configuration keywords

You can provide configuration keywords that the access method interrogates to tailor its behavior.

The user specifies one or more parameter choices in the USING clause of the CREATE TABLE statement. The access method calls the mi_tab_amparam() accessor function to retrieve the configuration keywords and values.

In the following example, the access method checks the keyword value to determine if the user wants mode set to the number of rows to store in a shared memory buffer. The CREATE TABLE statement specifies the configuration keyword and value between parentheses.

CREATE TABLE ...
IN sbspace
USING sbspace_access_method ("setbuffer=10")

In the preceding statement, the mi_tab_amparam() function returns setbuffer=10. The following figure shows how the access method determines the value that the user specifies and applies it to create the sbspace.

Figure 1: Checking a configuration parameter value

mi_integer my_beginscan (sd)
    MI_AM_SCAN_DESC    *sd;
{
   MI_AM_TABLE_DESC    *td;
   mi_integer             nrows;
   ...
   td=mi_scan_table(sd); /*Get table descriptor. */
   /*Check for parameter. 
   ** Do what the user specifies. */
   if (mi_tab_amparam(td) != NULL)
   {
      /* Extract number of rows from string. 
      ** Set nrows to that number. (not shown.) 
      */
      mi_tab_setniorows(nrows);
   }
   ...
}

Important: If the access method accepts parameters, describe them in the user guide for the access method. For example, a description of the action in Checking a configuration parameter value would explain how to set a value in the parameter string "setbuffer=" and describe how a buffer might improve performance.

A user can specify multiple configuration parameters separated by commas, as the following syntax shows:

CREATE TABLE ...
...
USING access_method_name (keyword='string', keyword='string' ...)