DOCUMENT:Q293638  22-JAN-2002  [foxpro]
TITLE   :BUG: Header Corruption Causes END TRANSACTION to Discard Appends
PRODUCT :Microsoft FoxPro
PROD/VER::5.0,5.0a,6.0
OPER/SYS:
KEYWORDS:kbDatabase kbvfp500 kbvfp500a kbvfp600 kbGrpDSFox kbDSupport

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The information in this article applies to:

 - Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a, 6.0 
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SYMPTOMS
========

An off-by-one record count in the header of a table may cause the END
TRANSACTION command to discard appended records with no error message displayed.

RESOLUTION
==========

If your tables are subject to this type of corruption, use a test as shown below
to compare the physical file size to the logical file size. Run this test when
you open the table.

STATUS
======

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

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

1. Copy the following code into a .prg file and then run it:

   LOCAL nRecCount, nLogicalSize, nPhysicalSize, nHandler, i

   CREATE DATABASE test_db
   CREATE TABLE test_tbl (one_field N(1,0))
   FOR i = 1 TO 5
   	INSERT INTO test_tbl (one_field) VALUES (i)
   ENDfor

   * Check size before corruption.
   SELECT test_tbl
   nRecCount = RECCOUNT()
   nLogicalSize = HEADER() + (nRecCount * RECSIZE()) + 1
   USE IN test_tbl

   nHandler = FOPEN('test_tbl.dbf', 2)
   nPhysicalSize = FSEEK(nHandler, 0, 2)
   FCLOSE(nHandler)

   ? 'BEFORE CORRUPTION'
   ? 'Record count: ', nRecCount
   ? 'Logical size: ', nLogicalSize
   ? 'Physical size:', nPhysicalSize

   * Manually decrease the record count in the table header.
   * Normally it would happen accidentally after some power 
   * or network failures.

   ?
   ? 'Simulating table corruption...'
   nHandler = FOPEN('test_tbl.dbf', 2)
   FSEEK(nHandler, 4)
   FWRITE(nHandler, CHR(4))
   FCLOSE(nHandler)

   * Check size after corruption
   USE test_tbl
   nRecCount = RECCOUNT()
   nLogicalSize = HEADER() + (nRecCount * RECSIZE()) + 1
   USE IN test_tbl

   nHandler = FOPEN('test_tbl.dbf', 2)
   nPhysicalSize = FSEEK(nHandler, 0, 2)
   FCLOSE(nHandler)

   ?
   ? 'AFTER CORRUPTION'
   ? 'Record count: ', nRecCount
   ? 'Logical size: ', nLogicalSize
   ? 'Physical size:', nPhysicalSize

   * I will try inserting a record within a transaction.

   ?
   ? 'Inserting new record...'

   USE test_tbl
   BEGIN TRANSACTION
   INSERT INTO test_tbl VALUES (6)
   END TRANSACTION
   ? 'No error:', ERROR()

   * Check size after insert
   nRecCount = RECCOUNT()
   nLogicalSize = HEADER() + (nRecCount * RECSIZE()) + 1

   USE IN test_tbl

   nHandler = FOPEN('test_tbl.dbf', 2)
   nPhysicalSize = FSEEK(nHandler, 0, 2)
   FCLOSE(nHandler)

   ?
   ? 'AFTER INSERTION'
   ? 'Record count: ', nRecCount
   ? 'Logical size: ', nLogicalSize
   ? 'Physical size:', nPhysicalSize

   ? 'VFP discarded insert operation.'
   CLOSE DATA ALL

Additional query words:

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Keywords          : kbDatabase kbvfp500 kbvfp500a kbvfp600 kbGrpDSFox kbDSupport 
Technology        : kbVFPsearch kbAudDeveloper kbVFP500 kbVFP600 kbVFP500a
Version           : :5.0,5.0a,6.0
Issue type        : kbbug
Solution Type     : kbpending

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