Memory Management in Visual FoxPro

• Microsoft Visual FoxPro for Windows, version 3.0

SUMMARY

This article describes memory management in Visual FoxPro. Memory is allocated in a page pool and a handle pool.

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Handle Pool

The handle pool contains memory that is used for various Visual FoxPro objects such as windows, menus, classes, objects, cursors, sessions, and so on. Unlike previous versions of FoxPro, this pool has no arbitrary limit. It is bound only by the amount of virtual memory available from the underlying operating system as set by the user using the operating system's virtual memory settings. Thus, the size and complexity of a user's form or application is limited only by available virtual memory, not available physical memory.

Page Pool

The page pool contains memory used for file caching (to perform read buffering), internal sorting, and query execution. For these purposes, it is critical that the memory be physical, not virtual. In other words, Visual FoxPro needs memory that won't be swapped to disk. While it can't guarantee this, it can try to ensure this by limiting the size of the page pool so that it will all fit in physical memory. The size of the page pool can also be set manually by using SYS(3050).

Note that MEMLIMIT is not used in Visual FoxPro. The handle pool is limited by available virtual memory, and the page pool can be dynamically resized using SYS(3050).