Record Blocking and Unblocking

By default, the RPG compiler unblocks input records and blocks output records to improve run-time performance in SEQ or DISK files when the following conditions are met:

1. The file is program-described or, if externally described, it has only one record format.
2. The keyword RECNO is not used in the file-description specification.
   Note:

   If RECNO is used, the ILE RPG compiler will not allow record blocking. However, if the file is an input file and RECNO is used, Data Management may still block records if fast sequential access is set. This means that updated records might not be seen right away.
3. One of the following is true:
   1. The file is an output file.
   2. If the file is a combined file, then it is an array or table file.
   3. The file is an input-only file; it is not a record-address file or processed by a record-address file; and uses only the OPEN, CLOSE FEOD, and READ file operations. (In other words, the following file operations are not allowed: READE, READPE, SETGT, SETLL, and CHAIN.)

The RPG compiler generates object program code to block and unblock records for all SEQ or DISK files that satisfy the above conditions. Certain IBM i system restrictions may prevent blocking and unblocking. In those cases, performance is not improved.

You can explicitly request record blocking by specifying the keyword BLOCK(*YES) on the file-description specification for the file. The only difference between the default record blocking and user-requested record blocking is that when BLOCK(*YES) is specified for input files, then the operations SETLL, SETGT and CHAIN can be used with the input file (see condition 3c above) and blocking will still occur. If the BLOCK keyword is not specified and these operations are used, no record blocking will occur.

You can also prevent the default blocking of records by specifying the keyword BLOCK(*NO) on the file-description specification. If BLOCK(*NO) is specified, then no record blocking is done by the compiler, nor by data management. If the keyword BLOCK is not specified, then default blocking occurs as described above.

The input/output and device-specific feedback of the file information data structure are not updated after each read or write (except for the RRN and Key information on block reads) for files in which the records are blocked and unblocked by the RPG compiler. The feedback area is updated each time a block of records is transferred. (For further details on the file information data structure see the IBM Rational Development Studio for i: ILE RPG Reference.)

You can obtain valid updated feedback information by preventing the file from being blocked and unblocked. Use one of the following ways to prevent blocking:

• Specify BLOCK(*NO) on the file description specification.
• At run time, use the CL command OVRDBF (Override with Database File) with SEQONLY(*NO) specified.