𝗖𝗢𝗕𝗢𝗟 𝗣𝗿𝗼𝗴𝗿𝗮𝗺 𝗔𝗯𝗲𝗻𝗱𝘀 𝘄𝗶𝘁𝗵 𝗦𝗕𝟯𝟳 𝗗𝘂𝗿𝗶𝗻𝗴 𝗖𝗟𝗢𝗦𝗘

A COBOL program successfully executes all its WRITE statements and reaches the CLOSE statement. Then, unexpectedly, the program issues an SB37 space abend.
 
Why would an out-of-space condition become visible during CLOSE rather than during WRITE?
 
Let's investigate.
 
The Test Program
 
Consider this simple COBOL program:
 
        IDENTIFICATION DIVISION.                                    
        PROGRAM-ID. TESTPGM.                                        
        ENVIRONMENT DIVISION.                                       
        CONFIGURATION SECTION.                                      
        SPECIAL-NAMES.                                              
        INPUT-OUTPUT SECTION.                                       
        FILE-CONTROL.                                               
            SELECT OUTPUT-FILE       ASSIGN TO OUTFILE.             
        DATA DIVISION.                                              
        FILE SECTION.                                               
        FD  OUTPUT-FILE.                                            
        01  OUTPUT-REC    PIC X(30).                                
        WORKING-STORAGE SECTION.                                    
        01 WS-GRP.                                                  
           05 FILLER         PIC X(05) VALUE 'WS-I:'.               
           05 WS-I           PIC S9(8) COMP.                        
        01 WS-VAR            PIC  9(8).                             
        PROCEDURE DIVISION.                                         
           ACCEPT WS-VAR                                            
           DISPLAY WS-VAR                                           
           OPEN OUTPUT OUTPUT-FILE                                  
           PERFORM VARYING WS-I FROM 1 BY 1 UNTIL WS-I > WS-VAR     
             WRITE OUTPUT-REC    
           END-PERFORM           
           DISPLAY 'WS-I ' WS-I  
           CLOSE OUTPUT-FILE     
           GOBACK.               
 
The program simply accepts a record count and writes that many 30-byte records.
 
The corresponding JCL is:
 
//GO1    EXEC  PGM=TESTPGM
//SYSOUT   DD  SYSOUT=*                                          
//OUTFILE  DD  DSN=USERID.TESTFIL,
//          LRECL=30,RECFM=FB,VOL=(,,,1),                       
//          DISP=(,CATLG,CATLG),
//          SPACE=(TRK,(1,1),RLSE),BUFNO=5   
//*                                                              
//SYSIN    DD *                                                  
00034520                                                         
//*                                                              
 
So the program attempts to write: 34,520 records
 
The important file allocation characteristics are:
 
LRECL = 30
BLKSIZE = 27,990
SPACE = TRK,(1,1) = 1 Primary + 15 secondary tracks = total 16 tracks
BUFNO = 5
 
First, Let's Look at the Blocks
 
With fixed-block records:
 
Records per block = BLKSIZE / LRECL = 27,990 / 30 = 933 records
 
Therefore, one physical block can contain 933 logical COBOL records.
 
For 34,520 records:  34,520 / 933 = 36 remainder 932
 
So the output consists of:

• 36 complete blocks
• 1 partial block containing 932 records

 
Therefore the output dataset needs space for 37 blocks.
 
A track can accommodate two blocks, and each block holds 933 records.
 
With 16 tracks available(based on SPACE parameter), the total number of records that can be successfully written to output file is:
 
16 tracks × 2 blocks per track × 933 records per block = 29,856 records
 
So, the output data set can accommodate exactly 29,856 records before the space-related failure occurs.
 
If we translate 29,856 records to number of blocks, 29856/933 = 32 blocks.
 
But program is trying to write 37 blocks of records.
 
Now Look at What the Program Reports
 
The SYSOUT contains:
 
00034520   

WS-I 00034521                            
IGZ0034W The file with system-name OUTFILE could not be extended.  Secondary extents were not specified or were not available.  The last WRITE was at offset X'E23156CC' in program TESTPGM.                                  
 
The interesting part is:  “WS-I 00034521”
 
This tells us that the PERFORM loop finished.  In other words, COBOL executed all 34,520 WRITE statements.
 
Yet, after the job abended, the output data set contained only 29,856 records.
 
This means that the remaining records were in BUFFER.
 
CLOSE Is More Than "Close the File"
 
Although all the WRITE statements have completed, some records are still held in the output buffers.
 
During CLOSE, these buffered records are written to disk.
 
Since the data set cannot be extended to accommodate them, the program encounters an SB37 abend while closing the file.