There are two main performance objectives for the remote journal
function. To provide a timely delivery of journal entries to a target system
and to minimize impacts to the journaling throughput on the source system.
Even though both aspects are very important for both synchronous
and asynchronous delivery modes, each mode prioritizes the two in a different
order. The top priority for synchronous delivery is to guarantee that the
remote journal is always up to date with the source journal. For asynchronous
delivery mode, the top priority is to minimize impacts to journaling throughput.
All
performance considerations that are currently used for a local journal still
apply and must continue to be employed. The following are additional factors
that may affect the performance of the remote journal function. The factors
are listed in the order of importance.
- Transport method
Your choice of transport
depends on the rate of the journal activity in your environment. Make special
consideration for using a fast transport method when you use synchronous delivery
mode. Weigh the response time impacts of the synchronous delivery mode in
your environment against the communications overhead of the transport method
you choose.
When replicating journal entries over a long distance, the
most important performance factors regarding a communications transport method
are the overall rated speed of the communications resource and any existing
traffic already using the communications resource.
For more information
about transport methods, see the Networking topic.
- Number of remote journals that are being maintained
With respect to the job performing the journal entry deposit, the
impact of the remote journal function for asynchronously maintained journals
is not noticeable. For synchronously maintained journals, the impact depends
on the slowest connection rather than number of remote journals.
The
impact to the job performing the journal entry deposit for an asynchronously
maintained journal is significantly less than that for a synchronously maintained
journal. Also, it is recommended that only one synchronous remote journal
be maintained for a given local journal.
With respect to the system
performance impacts, the processor use typically increases by less than an
equal factor for each additional remote journal.
- Arrival rate of journal entries that are being deposited on
the local system
The higher the arrival rate of journal
entries being deposited on the local system, the greater the chance journaling
throughput will increase for synchronous or asynchronous delivery. A high
arrival rate might cause asynchronous journaling to fall further behind.
- Batch versus interactive
In general, higher
local and remote journal throughput can be maintained when many interactive
jobs generate the journal throughput rather than a single-threaded batch job.
Journal caching can also increase this throughput for batch processing regardless
of the number of jobs.
- Processor utilization on the source system
The
higher the processor utilization of the source system, the greater the chance
of affecting journaling throughput for synchronous or asynchronous delivery.
This may cause asynchronous journaling to fall further behind.
- Processor utilization on the target system
The
higher the processor utilization of the target system, the greater the chance
of affecting journaling throughput for synchronous or asynchronous delivery.
This may cause asynchronous journaling to fall further behind.
- The value set for the sending task priority when using the asynchronous
delivery mode
The larger the value, the smaller effect the
remote journal function will have on the system, but the further the target
system may lag behind the source system.
Reducing the size of the journal receivers on the source
system will reduce the communications overhead of the remote journal function.
Therefore, you may want to consider journaling *AFTER images and not journaling
open, close, or force entries.