When the source server is an iSeries™ server, iSeries database functions can be used
on remote files. There are some restrictions, however.
The restrictions are:
- A source iSeries server can create
files on a System/38™, but the
DDM architecture file models are used. As a result, no multiformat logical
or join logical files can be created on a non-iSeries target
server, including a System/38.
- Save or restore operations do not save or restore the data on a target
server; only the DDM file object can be saved or restored locally.
- Operations that delay for a time period (that is, that wait for a file
or record) are determined by the time values specified on the target server.
(These values are specified by the WAITFILE and WAITRCD parameters on various
CL commands.) This can result in increased delay times when DDM is used to
access files or records remotely.
- Query requests (OPNQRYF) to a System/38 cannot
use group selection and join processing.
- When running System/36™ applications
to or from an iSeries server, these
applications might result in time-outs while waiting for a resource to become
available. When running System/36 applications
to or from another System/36,
the application waits indefinitely for the resource to become available.
For
both source and target DDM jobs, due to the way DDM sends APPC operations,
it is possible for the DDM job on the secondary side of the APPC conversation
to wait indefinitely after a line failure or other failures at the remote
server.
Consider the following suggestions to avoid indefinite waits:
- If the remote server supports record lock time-outs, ensure reasonable
time values are specified. For example, on a target iSeries server or System/38 database file, do not use maximum
values for CRTPF ... WAITRCD.
WAITRCD addresses read-for-update operations,
but does not apply to other file operations, such as read only, add, and so
on.
- When using an SDLC secondary line, use a time value for the line inactivity
timer (INACTTMR). Do not use the *NOMAX value.
- Provide the person responsible for server operation with the associated
line, controller, and device names (or a list of DDM jobs that might run).
If a DDM job then appears to be waiting indefinitely, this person can
display the job information to determine if the job is waiting indefinitely
by reviewing the job's processing unit time use (by using the Display
Job (DSPJOB) command to display the active run attributes).
When the target server is an iSeries server, iSeries database functions can be used
to access remote files, with the following restrictions:
- The physical files that the logical files or join logical files are based
on must exist on the same iSeries server.
- A logical file on a source iSeries server cannot
share the access path of a remote file (on any target server).
- Query requests (OPNQRYF), which require group selection and join processing
from a System/38, do not work.