Using the Realtime Monitor › Buffer I/O Summary (PF8)

Buffer I/O Summary (PF8)

 PM-Rnn.n SYSTEM71         CA, Inc.                  V71      08.348 10:44:07.23
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   02 Buffer I/O Summary                                                      >
                          Fnd_In     Read   Fnd_In    Write   Forced Prefetch
            Buffer_Name   Buffer    Count    Cache    Count    Write     Hits
   _ DBCR_BRCH_BUFFER        942        5                 1
   _ DBCR_ACCT_BUFFER        285      190       75        1
   _ LOG_BUFFER
   _ DEFAULT_BUFFER          541     1097                22

 PM-Rnn.n SYSTEM71         CA, Inc.                  V71      08.348 10:44:29.43
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   02 Buffer I/O Summary                                                   <
                         Write   Forced Prefetch      Bcr   Page  Buffer
          Buffer_Name    Count    Write     Hits    Waits   Size   Pages #Areas
 _ DBCR_BRCH_BUFFER          1                              4000     200      4
 _ DBCR_ACCT_BUFFER          1                              2932     200      5
 _ LOG_BUFFER                                               4276              1
 _ DEFAULT_BUFFER           22                              4276      30     24

Screen Description

The Buffer I/O Summary screen displays a line of information for each buffer defined to DC/UCF.

You can request a detailed display for a specific buffer, which breaks down the information for each file/area combination assigned to the buffer. Type any nonblank character in the select field to the left of the buffer name, then press [Enter]. The Realtime Monitor displays the Specific Buffer I/O Detail screen for each selected buffer.

What To Look For

• Look for a high number of read-request I/Os (Read Count) for a particular buffer, compared to the number of requested pages found in the buffer (Found In Buf). If this occurs, consider modifying the buffer's DMCL definition to:
  • Increase the number of pages in the buffer
  • Reassign areas to buffers based on their usage

  Note: By increasing the number or size of buffers, you decrease the amount of storage available to the DC/UCF system and may cause an increase in paging. If paging increases, decrease the size of the buffer.

• Look for a high value in the Forced Write field. A forced write occurs when the system must write a buffer page in order to read a database page. A high value means one of these conditions exist:
  • A long-running update job is not issuing COMMIT statements frequently enough
  • Buffer activity is excessive
• Look for a non-zero number in the BCR Waits field. A value in this field indicates a serious problem that can be remedied by increasing the number of pages in the buffer. The field is incremented when IDMSDBIO determines that all the pages in the buffer are exclusively held and must therefore wait until a buffer page becomes available.

You can determine if one file is responsible for a large percentage of buffer activity by requesting the Specific Buffer I/O Detail screen for the buffer.