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Space announcement We are no longer updating this space, and you cannot comment on this space. The IMAGE COPY PLUS component is now documented in BMC AMI Backup and Recovery for IMS.

Controlling the buffer pool size

The Image Copy utility can dynamically allocate an optimum number of buffers for input database and internal change accumulation work buffers based on the physical device and access method used.

You can also explicitly specify the number of buffers in the JCL.

The following keywords allow you to control the input buffer pool size.

  • DBBUF
  • NBUF

Procedures for database buffers

You can control buffer pool size for database buffers. The allocation of buffer pool sizes for database buffers depends on the access method used to read the data set group or area.

  1. When you use the native access method, as specified with DBACC(1), to read a data set group or area, you can control the number of buffers allocated by using the DBBUF keyword, JCL specifications, and VSAM catalog definitions. All buffers for the non-VSAM native access method are allocated below the 16 MB line.
    1. Specify the DBBUF keyword on a valid control statement or in an options module. The value you specify with the DBBUF keyword is used to calculate the number of buffers to allocate.
    2. For an OSAM data set, if you specify DCB=BUFNO=n on the input data set DD statement, and if this value is larger than the value calculated using the DBBUF keyword, this value overrides the DBBUF keyword.

    3. For a VSAM data set, if you specify AMP=(‘BUFND=n’) on the input data set DD statement, this value always overrides the DBBUF keyword. If you do not specify this value in the JCL, and if the value specified in the catalog using the BUFSPACE parameter is larger than the value calculated using the DBBUF keyword, this value overrides the DBBUF keyword.

      For a VSAM KSDS or an ESDS overflow data set, buffers are always allocated based on the number of CIs per CA.

  2. When you use the EXCP access method, specified with DBACC(2), to read a data set group or area, enough buffers to hold two cylinders of input data are always allocated. All buffers for the EXCP access method are allocated above the 16 MB line.
  3. When you use the start I/O access method, specified with DBACC(3), to read a data set group or area, enough buffers to hold two cylinders of input data are always allocated. These buffers are allocated in PAGE FIXED storage, which is above the 16 MB line.


Procedures for image copy and change accumulation buffers

The utility manages buffers automatically for input image copy and change accumulation data sets.

The utility dynamically allocates an optimum number of buffers for input image copy and change accumulation data sets based on the physical device and block size used. All buffers are allocated above the 16 MB line.

In previous versions of the utility, the DSBUF keyword was used to control the buffer pool size. This keyword is still accepted if it is specified with a valid value on a control statement or in an options module, but its value is ignored.

If you specify DCB=BUFNO=n on the input data set DD statement, the utility ignores the specification.

Related topic

Controlling-input


 

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IMAGE COPY PLUS 5.1