10.4 Page at a Time Scrolling

The following RDML program generically searches for employees by surname.  The user specifies all or part of an employee's surname and a resulting list of employees with names matching the request is displayed.

********   Define work variables and browse list to be used

DEFINE     FIELD(#L1COUNT) TYPE(*DEC) LENGTH(7) DECIMALS(0)

DEF_LIST   NAME(#L1) FIELDS((#SURNAME) (#GIVENAME) (#EMPNO)

#ADDRESS1)) COUNTER(#L1COUNT)

********   Loop until terminated by EXIT or CANCEL

BEGIN_LOOP

********   Get surname to search for

REQUEST    FIELDS(#SURNAME)

********   Build list of generically identical names

CLR_LIST   NAMED(#L1)

SELECT     FIELDS(#L1) FROM_FILE(PSLMSTV1)

           WITH_KEY(#SURNAME) GENERIC(*YES)

ADD_ENTRY  TO_LIST(#L1)

ENDSELECT

********   If names found, display list to user

IF          COND('#L1COUNT *GT 0')

DISPLAY    BROWSELIST(#L1)

********   else issue error indicating none found

ELSE

MESSAGE    MSGTXT('No employees have a surname matching request')

ENDIF

********   Loop back and request next name to search for

END_LOOP

This program will work just fine, but what if the user inputs a search name of "D", and 800 employees working for the company have a surname that starts with "D".

The result will be a list containing 800 names. But more importantly, it will take a long time to build up the list and use a lot of computer resource while doing it.

To solve this problem, a technique called "page at a time" browsing is often used.

What this means is that the program extracts one "page" of names matching the request, and then displays them to the user. If the user presses the roll up key then the next page is fetched and displayed, etc, etc.

The following program is functionally identical to the first example, but produces the same results in a much shorter time and with less use of computer resources.

New or modified commands are indicated by -->.

    ********   Define work variables and browse list to be used

    DEFINE     FIELD(#L1COUNT) TYPE(*DEC) LENGTH(7) DECIMALS(0)

--> DEFINE     FIELD(#L1PAGE) TYPE(*DEC) LENGTH(7) DECIMALS(0)

--> DEFINE     FIELD(#L1TOP) TYPE(*DEC) LENGTH(7) DECIMALS(0)

--> DEFINE     FIELD(#L1POS) TYPE(*CHAR) LENGTH(7)

--> DEF_LIST   NAME(#L1) FIELDS((#SURNAME) (#GIVENAME) (#EMPNO) (#ADDR+

               ESS1)) COUNTER(#L1COUNT) PAGE_SIZE(#L1PAGE) TOP_ENTRY(#+

               L1TOP) SCROLL_TXT(#L1POS)

    ********   Loop until terminated by EXIT or CANCEL

    BEGIN_LOOP

    ********   Get surname to search for

    REQUEST    FIELDS(#SURNAME)

    ********   Build list of generically identical names

    CLR_LIST   NAMED(#L1)

--> CHANGE     FIELD(#IO$KEY) TO(UP)

--> CHANGE     FIELD(#L1TOP) TO(1)

--> SELECT     FIELDS(#L1) FROM_FILE(PSLMSTV1)

               WITH_KEY(#SURNAME) GENERIC(*YES)

-->            WHERE('#IO$KEY = UP') OPTIONS(*ENDWHERE)

--> EXECUTE    SUBROUTINE(DISPLAY) WITH_PARMS('''More...''')

    ADD_ENTRY  TO_LIST(#L1)

    ENDSELECT

     ********   If names found, display list to user

    IF        COND('#L1COUNT *GT 0')

--> EXECUTE    SUBROUTINE(DISPLAY) WITH_PARMS('''Bottom''')

     ********   else issue error indicating none found

    ELSE

    MESSAGE    MSGTXT('No employees have a surname matching request')

    ENDIF

    ********   Loop back and request next name to search for

    END_LOOP

    ********

    ********   Display names if page is full or list is complete

      ********

--> SUBROUTINE NAME(DISPLAY) PARMS(#L1POS)

--> DEFINE     FIELD(#L1REMN) TYPE(*DEC) LENGTH(5) DECIMALS(5)

--> CHANGE     FIELD(#L1REMN) TO('#L1COUNT / #L1PAGE')

--> IF        COND('(#L1COUNT *NE 0) *AND (#IO$KEY = UP) *AND ((#L1PO+

              S = ''Bottom'') *OR (#L1REMN *EQ 0.00000))')

--> DOUNTIL    COND('(#L1POS *NE ''Bottom'') *OR (#IO$KEY *NE UP)')

--> DISPLAY    BROWSELIST(#L1) USER_KEYS((*ROLLUP))

--> ENDUNTIL

--> CHANGE     FIELD(#L1TOP) TO('#L1TOP + #L1PAGE')

--> ENDIF

--> ENDROUTINE

The "page at a time" technique described here can be applied to just about any situation where a browse list is used and can considerably improve performance in most of them.

It is easy to modify existing programs that use SELECT and DISPLAY (like the initial example here) to use the page at a time technique. Note how the new logic "slots into" the existing logic with no major structural change to the program logic/flow.

The easiest way to implement "page at a time" techniques is to design and fully test a standard "algorithm" that is suitable for your site's needs.

This should then be set up as an Application Template so that it is accessible to all RDML programmers.