BUG: Large Result Sets May Become Corrupted in VFP

When using a cursor or view against an external table like those in SQL Server or any other server, the local representation of the records at the end of the result set may become corrupted. Data on the server itself is not affected. Occurrence of the corruption varies with the size of the result set and the settings of SYS(3050). Corruption may also occur with the default settings for SYS(3050). Corruption occurs after switching to another program or bringing up a new window like the Class Browser.

Following are some suggestions to avoid this problem:

1. Maximize the buffer size by setting both SYS(3050,1) and SYS(3050,2) to the value of SYS(1001).
2. Do not use Class Browser concurrently or have projects or designers open when using these queries or views, and, where possible, avoid moving other application windows in front of Visual FoxPro during use of these cursors.
3. Test cursor or view for the presence of corruption with the following command:

         LOCATE FOR AT(CHR(0))
   					

4. Install more memory.
5. Work with smaller cursors, bringing down a smaller subset of the data.
6. Limit the number of cursor open at any given time.

Microsoft has confirmed this to be a problem in the Microsoft products listed at the beginning of this article.

NOTE: This problem is rare and isolated to the specific conditions described in this article.

Corruption depends upon available memory, the setting, if any, of SYS(3050), the number of records, number of fields and size of the fields. It seems that only very specific combinations cause the error. Changing a field size or adding or deleting a field may resolve the problem.