DFHLSCU is a migration utility that helps you to define your CICS® Transaction Server for z/OS®, Version 3 Release 1 log
streams, based on your CICS/ESA 4.1 or CICS/ESA 3.3 journaling activity. It examines
one or more CICS/ESA 4.1 or CICS/ESA 3.3 journal data sets, and produces a report
directed to SYSPRINT. The report contains a summary for every interval (as
specified on the INTERVAL SYSIN statement), showing the largest calculated
AVGBUFSIZE. The end of the report provides conclusions and recommendations.
The conclusion of the report is divided into two sections, dealing with the
CF log stream and the DASD-only log stream.
Note:
If you plan to define all your log streams as DASD-only, but
there is a possibility that, at a later date, you might want to convert some
of them to CF log streams, it is a good idea to save the output from DFHLSCU
for later reference.
The values provided by DFHLSCU are estimates and
may not match your actual experience. In particular, they may be affected
by changes in the pattern of logging such as:
- RLS file usage moving logging from an FOR into AORs.
- Combining journals onto a single log stream.
- Introducing more cloned AORs.
While the recommended values provide a starting point for structure sizing,
you should monitor actual usage and adjust it as required.
The first section of the report’s conclusion assumes that you want
to define a log stream that uses a coupling facility structure. For a CF log
stream, the report provides the following information (see below for descriptions
of the attributes involved):
- The largest calculated AVGBUFSIZE.
- A sample definition for the log stream structure. The definition contains
recommended values for:
- A sample definition for CF space required for the log stream. The definition
contains recommended values for:
- A sample log stream definition. The definition contains recommended values
for:
- For a CF log stream that will use duplexing, a recommended size for the
staging data set.
You must edit the sample definitions and provide appropriate values for
the structure name and preflist name. See Sample report from DFHLSCU for an example
of the output from DFHLSCU.
The attributes for which the report provides recommended values are explained
as follows:
- AVGBUFSIZE
- The average buffer size, in bytes, of a log stream structure in the
coupling facility. It is important, particularly in MVS™ releases before OS/390® Release 3,
that the value you specify for AVGBUFSIZE reflects as accurately as possible
the real size of most log blocks written to the structure. This leads to efficient
use of the space in the coupling facility and minimum DASD offloading frequency.
This is less important in OS/390 Release 3 and later, because OS/390 performs
some dynamic tuning.
- INITSIZE
- The initial amount of space, in kilobytes, to be allocated for the log
stream structure in the coupling facility. You define this attribute in your
CFRM policy.
- HIGHOFFLOAD
- The point in primary storage (that is, in either the coupling facility
structure or the staging data set), as a percentage of space consumed, at
which the MVS system logger starts its offload process--which can cause data from
the log stream to be offloaded to log stream DASD data sets. (The offload
process is described in the CICS Transaction Server for z/OS Installation Guide.) You define
this attribute in your DEFINE LOGSTREAM job.
- LOWOFFLOAD
- The point in primary storage, as a percentage of space consumed, at
which the MVS system logger stops offloading data from the log stream to log stream DASD
data sets. You define this attribute in your DEFINE LOGSTREAM job.
- MAXBUFSIZE
- The size, in bytes, of the largest block of data that can be written
to the log stream.
- SIZE
- The maximum size, in kilobytes, of the log stream structure in the coupling
facility. You define this attribute in your CFRM policy.
- STG_SIZE
- Optionally, a staging data set can be used with a CF log stream. For
guidance about when to use a staging data set, see the CICS Transaction Server for z/OS Installation Guide. STG_SIZE is the size, as a number of 4K blocks, of the
staging data set, if one is required. You define this attribute in your DEFINE
LOGSTREAM job.
The second section of the report’s conclusion assumes that you want
to define a log stream that uses DASD-only logging. It provides a sample log
stream definition which contains recommended values for the following attributes
(all of which are defined in your DEFINE LOGSTREAM job):
- HIGHOFFLOAD
- LOWOFFLOAD
- MAXBUFSIZE
- STG_SIZE
See Sample report from DFHLSCU for an example of the output from DFHLSCU.
The attributes for which the report provides recommended values are explained
as follows:
- HIGHOFFLOAD
- The point in primary storage (that is, in the staging data set), as
a percentage of space consumed, at which the MVS system logger starts its offload process.
- LOWOFFLOAD
- The point in primary storage as a percentage of space consumed, at which
the MVS system logger stops offloading data from the log stream to log stream DASD data
sets.
- MAXBUFSIZE
- The size, in bytes, of the largest block of data that can be written
to the log stream.
- STG_SIZE
- The size, as a number of 4K blocks, of the staging data set for the
log stream.
A DASD-only log stream always uses a staging data set.
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