When fast commit is enabled, requests that each active database
process on each node flush updated database pages from its buffer
pool to disk.
1 – Description
Usually, each process performs a checkpoint operation after a
certain set of thresholds has been exceeded. The RMU Checkpoint
command allows you to spontaneously force each process to perform
a checkpoint operation.
Performing a checkpoint operation is useful for several purposes.
A checkpoint operation with the Wait qualifier causes all updated
database pages to be flushed to disk. A checkpoint operation
also improves the redo performance of the database recovery (DBR)
process (although the per-process parameters should have already
been properly initialized with this goal in mind).
When the Checkpoint command with the Wait qualifier completes
(the system prompt is returned), all active processes have
successfully performed a checkpoint operation.
When the system prompt is returned after you issue the Checkpoint
command with the Nowait qualifier, there is no guarantee that
all active processes have successfully performed a checkpoint
operation.
2 – Format
(B)0[mRMU/Checkpoint root-file-spec
[4mCommand[m [4mQualifiers[m x [4mDefault[m
x
/[No]Wait[/Until=date-and-time] x /Wait
3 – Parameters
3.1 – root-file-spec
The root file specification for the database you want to
checkpoint. You can use either a full or partial file
specification, or a logical name.
If you specify only a file name, Oracle Rdb looks for the
database in the current default directory. If you do not specify
a file extension, Oracle Rdb assumes a file extension of .rdb.
4 – Command Qualifiers
4.1 – Wait
Wait[/Until]
Nowait
Specifies whether or not the system prompt is to be returned
before the checkpoint operation completes.
When you specify the Wait qualifier without the Until qualifier,
the system prompt is not returned to you until all processes have
flushed updated database pages to disk. The Wait qualifier is the
default.
Used with the Wait qualifier, the Until qualifier specifies the
time at which the RMU Checkpoint/Wait command stops waiting
for the checkpoint and returns an error message. If you do not
specify the Until qualifier, the wait is indefinite.
When you specify the Nowait qualifier, the system prompt
is returned immediately, before all processes have flushed
database pages to disk. In addition, when you specify the Nowait
qualifier, there is no guarantee that all processes will flush
their database pages to disk.
The Nowait qualifier is useful when it is more essential that the
system prompt be returned immediately than it is to be certain
that all processes have checkpointed.
5 – Usage Notes
o To use the RMU Checkpoint command for a database, you must
have the RMU$BACKUP or RMU$OPEN privilege in the root file
access control list (ACL) for the database or you must have
the OpenVMS WORLD privilege.
o The RMU Checkpoint command is useful only if the database fast
commit feature has been enabled. If the fast commit feature is
disabled, this command does nothing.
For more information on the fast commit feature, see the FAST
COMMIT IS ENABLED section of the SQL ALTER DATABASE statement
in the Oracle Rdb SQL Reference Manual.
6 – Examples
Example 1
The following command causes all the active database processes on
all nodes to immediately perform a checkpoint operation:
$ RMU/CHECKPOINT MF_PERSONNEL.RDB
Example 2
The following command requests that all the active database
processes on all nodes perform a checkpoint operation and that
the system prompt be returned to you immediately. In this case,
there is no guarantee that all processes will actually perform a
checkpoint operation.
$ RMU/CHECKPOINT/NOWAIT MF_PERSONNEL.RDB