PRB: FoxPro/Mac Table Operations Do Not Release Memory

• Microsoft Visual FoxPro for Macintosh, version 3.0b
• Microsoft FoxPro for Macintosh, version 2.6a

SYMPTOMS

User object memory in FoxPro increases greatly and does not decrease when you issue any of the following commands on a large table:

   DELETE ALL
   RECALL ALL
   INDEX ON
   SCAN...ENDSCAN

RESOLUTION

Closing and reopening the table reduces memory usage back to its approximate original value.

STATUS

Microsoft is researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

User object memory is defined as memory used by objects that the user or programmer defines. User-defined objects include user-defined windows, menu bars, menus, variables, arrays, open tables, files opened with low-level file functions, and so on. User object memory can be checked with the SYS(1016) function.

Applications on the Macintosh obtain memory from the operating system in a different way than Windows applications. On the Macintosh, the amount of memory to be allocated to a program is specified in the Get Info window under the Mac's File menu. The minimum amount of memory to be used for an application and the preferred amount can be set. However, the application must be closed to change these settings. If there is enough memory for the preferred amount to be used, the application takes this much memory from the operating system upon startup although the application may not be using all that memory. The memory is just reserved for the application.

In addition to using the SYS(1016) function, the amount of memory allocated to FoxPro that is in use can be viewed from the About This Computer (or About This Macintosh, depending on the System software version) command on the Apple menu in Finder. This dialog box displays the System software version, the amount of total memory, the amount of virtual memory and the memory allocated to all running applications, including Finder itself. If Balloon Help is turned on and the mouse pointer is placed over the memory bar for an application, the balloon displays the amount of memory in use by the application. For instance, with Visual FoxPro, the balloon may display "This program is currently using 2.8 MB out of the 5.9 MB reserved for it."

Steps to Reproduce Behavior

1. Obtain or create a large table. The program below can be used to create a large table with 90,000 records. This may take considerable time to run depending on the speed of the Macintosh.

         CREATE TABLE BigTable (CharVal C(12), NumVal N(8.0))
         USE BigTable.DBF
         FOR x = 1 TO 90000
         INSERT INTO bigtable (CharVal, NumVal) ;
            VALUES (SYS(2015), RECCOUNT()+1)
         NEXT
         USE
   
   

2. Check user object memory with the SYS(1016) function. From the Command window type in the code below and then press ENTER:

         ? SYS(1016)
   

   A number should appear on the FoxPro screen.

   Here is an example:

         2516480
   

3. In the Command window type:

         USE Big_Table
         ? SYS(1016)
   

   The User object memory should increase slightly.

4. Issue a DELETE ALL command in the Command window and check SYS(1016) again.

5. Now issue a RECALL ALL in the Command window and check SYS(1016).

6. Close the table by issuing just the USE command in the Command window and check SYS(1016).

7. Similar results can be seen using the INDEX ON command and a SCAN...ENDSCAN loop. The INDEX ON <fieldname> TO <filename.idx> command uses more memory than the DELETE ALL or RECALL ALL commands.

REFERENCES

For more information on creating large tables for testing purposes, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q170128
   TITLE     : HOWTO: Programmatically Create Large Tables for Testing
               Purposes

Keywords          : FoxMac FxenvMemory FxprgTable VFoxMac
Version           : MACINTOSH:2.6a,3.0b
Platform          : MACINTOSH
Issue type        : kbprb