ISAM INSERT with Duplicate Key Incorrectly Allocates Record (62460)


The information in this article applies to:

  • Microsoft Basic Professional Development System for MS-DOS 7.0
  • Microsoft Basic Professional Development System for MS-DOS 7.1
This article was previously published under Q62460

SYMPTOMS

When you specify a unique key with CREATEINDEX using Microsoft Basic Professional Development System (PDS) version 7.00 ISAM, inserting records with duplicate keys causes a trappable error (run-time error 86). However, the ISAM engine still inserts one record into the ISAM file per attempt to insert a duplicate key record. The records inserted with the duplicate keys are marked as deleted. The Basic function LOF, which returns the total number of records in a Basic PDS 7.00 ISAM file, will show the actual number of successful writes to the file, showing that the records written with duplicate keys are not valid. Since these records are marked as deleted, using the ISAMPACK utility will remove the records and reduce the file to its appropriate size.

STATUS

Microsoft has confirmed this to be a bug in Microsoft Basic Professional Development System (PDS) versions 7.00 and 7.10 for MS-DOS. We are researching this problem and will post new information here as it becomes available.

MORE INFORMATION

The sample program below demonstrates the problem. If you execute the code below, a record will be inserted into the ISAM file, and then 999 more attempts will be made to insert that record. Since the program specifies unique keys in the CREATEINDEX statement, run-time error 86, "Duplicate key," will occur. The program will trap the "Duplicate key" error and resume execution. When the program terminates, the LOF function will show there is only one legitimate record in the file. The file size, however, will be approximately 1.6 MB. Using ISAMPACK.EXE on the ISAM file created by the program will reduce the file to 64K in size.

To execute the program below, you must load the Basic PDS 7.00 or 7.10 ISAM support by executing the PROISAMD.EXE TSR (terminate-and-stay- resident) program. After PROISAMD has been loaded, you can execute the program within the QBX.EXE environment.

Code Example

'WARNING: Even though this program only successfully
'         writes one ISAM record, it creates a 1.6 MB file.
TYPE NewRec
   AString AS STRING * 8
END TYPE

40 ON ERROR GOTO errorhandler
50 DIM NewBuf AS NewRec
60 OPEN "output.mdb" FOR ISAM NewRec "NewRec" AS #1

70 CREATEINDEX #1, "X", 1, "AString"    '* Specify unique key *

80 NewBuf.AString = "ABCDEFGH"
90 FOR i = 1 TO 1000
100     INSERT #1, NewBuf      '* Causes 999 "Duplicate key" errors *
110    PRINT i
120 NEXT
130 PRINT "Size of database (should be 1): "; LOF(1)
135 DELETEINDEX #1, "X" ' Delete the index so the program
                        ' can be run over.
140 END

errorhandler:
150     SELECT CASE ERR
            CASE 86: PRINT "duplicate key attempted":
            RESUME NEXT
        CASE ELSE
            CLS
            PRINT "An error occurred. The number is: "; ERR
            PRINT "It occurred on line: "; ERL
            DELETEINDEX #1, "X"
            END
        END SELECT
Modification Type:MinorLast Reviewed:8/16/2005
Keywords:KB62460
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