PL/I 语言文件读写优化实战：减少磁盘 I/O 操作
PL/I（Programming Language One）是一种高级程序设计语言，它结合了多种编程语言的特性，旨在提高编程效率和程序的可移植性。在处理大量数据时，磁盘 I/O 操作往往成为性能瓶颈。本文将围绕PL/I语言，探讨如何通过代码优化减少磁盘 I/O 操作，提高文件读写效率。
文件读写优化原理
在PL/I中，文件读写操作通常通过`OPEN`、`READ`、`WRITE`和`CLOSE`等语句实现。以下是一些减少磁盘 I/O 操作的优化原理：
1. 批量读写：通过一次性读取或写入多个数据块，减少磁盘访问次数。
2. 缓冲区优化：合理设置缓冲区大小，减少实际磁盘访问次数。
3. 顺序访问：尽量使用顺序访问方式，避免随机访问带来的性能损耗。
4. 预分配空间：在文件创建时预分配足够的空间，避免后续扩展文件时频繁的磁盘操作。
代码示例
以下是一些PL/I代码示例，展示了如何通过优化减少磁盘 I/O 操作。
批量读写
pl/i
IDENTIFICATION DIVISION.
PROGRAM-ID. BATCH-READ-WRITE.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT INPUT-FILE ASSIGN TO "input.dat"
ORGANIZATION IS SEQUENTIAL
ACCESS MODE IS SEQUENTIAL.
SELECT OUTPUT-FILE ASSIGN TO "output.dat"
ORGANIZATION IS SEQUENTIAL
ACCESS MODE IS SEQUENTIAL.
DATA DIVISION.
FILE SECTION.
FD INPUT-FILE.
01 INPUT-RECORD.
05 FILLER PIC X(100).
FD OUTPUT-FILE.
01 OUTPUT-RECORD.
05 FILLER PIC X(100).
WORKING-STORAGE SECTION.
01 BUFFER.
05 BUFFER-RECORDS OCCURS 100 TIMES.
10 BUFFER-REC PIC X(100).
PROCEDURE DIVISION.
OPEN INPUT INPUT-FILE OUTPUT OUTPUT-FILE.
PERFORM UNTIL END-OF-FILE
READ INPUT-FILE INTO BUFFER-RECORDS
IF NOT END-OF-FILE
PERFORM UNTIL END-OF-FILE OR 100 > 0
WRITE OUTPUT-FILE FROM BUFFER-REC
SUBTRACT 1 FROM 100
END-PERFORM
END-IF
END-PERFORM.
CLOSE INPUT-FILE OUTPUT-FILE.
缓冲区优化
pl/i
IDENTIFICATION DIVISION.
PROGRAM-ID. BUFFER-OPTIMIZE.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT INPUT-FILE ASSIGN TO "input.dat"
ORGANIZATION IS SEQUENTIAL
ACCESS MODE IS SEQUENTIAL.
SELECT OUTPUT-FILE ASSIGN TO "output.dat"
ORGANIZATION IS SEQUENTIAL
ACCESS MODE IS SEQUENTIAL.
DATA DIVISION.
FILE SECTION.
FD INPUT-FILE.
01 INPUT-RECORD.
05 FILLER PIC X(100).
FD OUTPUT-FILE.
01 OUTPUT-RECORD.
05 FILLER PIC X(100).
WORKING-STORAGE SECTION.
01 BUFFER.
05 BUFFER-RECORD PIC X(100).
05 BUFFER-INDEX PIC 9(4) VALUE 0.
PROCEDURE DIVISION.
OPEN INPUT INPUT-FILE OUTPUT OUTPUT-FILE.
PERFORM UNTIL END-OF-FILE
READ INPUT-FILE INTO BUFFER-RECORD
IF NOT END-OF-FILE
PERFORM UNTIL BUFFER-INDEX = 0
WRITE OUTPUT-FILE FROM BUFFER-RECORD
SUBTRACT 1 FROM BUFFER-INDEX
END-PERFORM
END-IF
END-PERFORM.
CLOSE INPUT-FILE OUTPUT-FILE.
预分配空间
pl/i
IDENTIFICATION DIVISION.
PROGRAM-ID. PREALLOCATE-SPACE.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT OUTPUT-FILE ASSIGN TO "output.dat"
ORGANIZATION IS SEQUENTIAL
ACCESS MODE IS SEQUENTIAL.
DATA DIVISION.
FILE SECTION.
FD OUTPUT-FILE.
01 OUTPUT-RECORD.
05 FILLER PIC X(100).
WORKING-STORAGE SECTION.
01 FILE-LENGTH PIC 9(9) VALUE 1000000.
PROCEDURE DIVISION.
OPEN OUTPUT OUTPUT-FILE.
PERFORM UNTIL FILE-LENGTH = 0
WRITE OUTPUT-FILE FROM OUTPUT-RECORD
SUBTRACT 1 FROM FILE-LENGTH
END-PERFORM.
CLOSE OUTPUT-FILE.
总结
通过以上代码示例，我们可以看到在PL/I语言中，通过批量读写、缓冲区优化和预分配空间等策略，可以有效减少磁盘 I/O 操作，提高文件读写效率。在实际应用中，应根据具体需求选择合适的优化方法，以达到最佳性能。
Comments NOTHING