Request WF2 Support

Learn to request WF2 support with Datacom VSAM Transparency.
WF2 support facilitates the sequential processing of high-volume MDB files which are opened for input. WF2 support is not available for MDB files that are opened for output or for files being read backwards.

VIT Requirements for WF2 Support

MDB-related tables are defined in the VSAM Interface Table (VIT) through the set of
DBVUFIL
macros for the base cluster and associated paths of the source VSAM file. You can request WF2 support for the MDB-related tables when processed through the base cluster or any path. If processed through a path, the alternate key need not be unique.
DBVUFIL
parameter specifications for requesting WF2 support follow:
  • WF2=
    YES
    (required)
  • MDB=
    YES
    (required)
  • STRNO=
    1
    or
    STRNO=
    ACB
    , if ACB specifies or defaults to a maximum of one string (required)
  • Specify a
    SEQBUF=
    value to provide more buffers for read-ahead processing.
  • GETBLK=
    and
    GBMAXR=
    with valid values greater than 0 in
    DBVUFIL
    or in
    DBVUEND
    .

Comparison of Processing with and without WF2 Support

When sequentially processing MDB-related tables
without
WF2 support, the Transparency uses generic table access. That is, it issues locate requests to
Datacom/DB
with only the common key name and DBID rather than with the table name.
Datacom/DB
locates the next record based on Index Area (IXX) entries and returns the name of the table in which the next record resides and the record ID of the key. The Transparency then issues a read request using the returned location information to access the required record. Thus, after initial positioning, two commands are issued for each record read: a generic
LOCNX
command and a
REDLE
(read located entry) command.
When processing MDB-related tables
with
WF2 support, the Transparency eliminates locates (LOCxx) before all reads (GETITs) by tracking the lowest value in each table which has not been processed and making comparisons among these low values to locate the next sequential record. That is, the Transparency determines the next logical record rather than issuing a command for
Datacom/DB
to make that determination.
WF2 processing is to multiple tables converted from a single VSAM file what GETIT processing is to a single table converted from a VSAM file. A large, batch MDB file can be read sequentially according to the defined Native Key much more quickly with WF2 support than without. Processing efficiency approaches that which can be realized when sequentially reading a non-MDB file of the same size with GETIT support. WF2 implements read-ahead buffering to significantly reduce the number of Data I/O operations. WF2 processing can be applied to only one MDB file per program at a time.
To ensure that tables that are converted from a particular VSAM file are eligible for read-ahead buffering, code
WF2=
YES
in the
DBVUFIL
macro for the batch VSAM Interface Table definition of the VSAM file identified by
VSAMNM=
. Specify the number of buffers to use for read-ahead processing with the
SEQBUF=
parameter and modify
GETBLK=
and
GBMAXR=
accordingly. The
SEQBUF=
value you specify applies to each MDB table. For example, if you specify
SEQBUF=
4
for an MDB file that is converted to five tables, WF2 uses 20 sequential buffers for the processing of this file. The
GETBLK=
and
GBMAXR=
values you specify apply to each MDB table as well, for example, if you specify
GETBLK=
29696
and
GBMAXR=
120
for this MDB file, WF2 requests
DBINFPR
to allocate five buffers of 29K bytes each in the user area, or 145K of buffer space, where the buffers accommodate a maximum of 120 records each, or a maximum of 600 records. The Transparency's internal WF2 buffer table contains five records, five Request Areas, and control information.

WF2 Resource Allocation when WF2=YES

When the Transparency processes the VSAM OPEN request to a converted file, it evaluates the processing options that are specified in the file's ACB and in the file's
DBVUFIL
macro in the VSAM Interface Table (VIT). It also examines the current utilization of resources. When read-ahead buffering is requested and all VIT Requirements for WF2 Support have been met, the Transparency allocates the WF2 resource for processing the tables that are converted from the file being opened only under the following conditions:
  • The file's ACB contains the following specifications:
    • MACRF=
      IN
      is specified (read-only processing is permitted).
    • MACRF=
      OUT
      is not specified (update processing is not permitted).
    • MACRF=
      SEQ
      is specified (sequential processing is permitted).
    • Neither
      MACRF=
      DIR
      nor
      MACRF=
      SKP
      is specified (neither direct-access nor skip-sequential access is permitted).
  • The current resource availability is as follows:
    • WF2 processing is not currently active for another file.
    • Space for the WF2 buffer table is available.