RDF/IMP and IMPX System Management Manual (RDF 1.4+)

Introducing RDF
HP NonStop RDF/IMP and IMPX System Management Manual—524388-001
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Extractor Process
When the extractor has no information to send from the audit trail, it transmits a buffer
containing no audit images (an empty buffer) to the receiver. When it receives an
empty buffer, the receiver process generates an RDF control-point record in each
image trail. Therefore, even when no TMF transactions are generated on the primary
system, RDF adds internal control points to the image trail on the backup system. The
file-filling rate for RDF control point records is very slow and is normally not noticeable.
Although the extractor runs as a process pair, the primary process does not maintain
restart information nor checkpoint this information to its backup. Instead, the receiver
maintains all restart information for the extractor, ensuring that the extractor is
restartable. The restart point is based on the MAT position of the last record safely
stored in the image trail on the backup system.
Whenever you start RDF, the extractor requests its starting position in the audit trail
from the receiver. Because this position is based on the audit trail position of the last
image record safely stored in the image trail by the receiver, this method guarantees
that no audit is mistakenly omitted. If the primary extractor process fails, the backup
process requests from the receiver a new starting position in the audit trail, further
guaranteeing a correct restart position. This extractor-receiver protocol also provides
protection against messages from the extractor erroneously arriving out-of-order: if a
message arrives out-of-order, the receiver directs the extractor to restart.
When it reads from an audit trail file, the extractor pins the file by sending a message
to TMF. Once pinned, an audit trail file remains pinned until the extractor unpins it or
you issue the following RDFCOM command at the primary system:
UNPINAUDIT
If you unpin files, RDF cannot be restarted if the files required by the extractor cannot
be made available. When you unpin audit trail files, be sure that these files are dumped
to disk or tape. If they are not dumped, and the TMP renames the file or files required
by the extractor, you will have to reinitialize RDF and resynchronize the primary and
backup databases.
In response to the UNPINAUDIT command, RDFCOM issues a prompt asking you to
confirm your request.
If the files are unpinned successfully, RDFCOM issues an informational message to
that effect.
If an error occurs while attempting to unpin the audit trail files, the command is ignored,
and RDFCOM issues a message indicating the error.
Note. Except for PURGEDATA, RDF does not replicate NonStop SQL DDL operations on
tables. For more information about NonStop SQL DDL operations and databases on a system
protected by the RDF product, see NonStop SQL Databases
.
Caution. Before deleting an RDF configuration, always issue an UNPINAUDIT command to
unpin any audit trail files that might be pinned by the configuration. If you delete the
configuration without first doing so, then you will be unable to unpin the files afterward.