Journaling is enabled by default for the SAS Metadata
Server. For best performance, it is recommended that journaling be
enabled at all times. In addition, journaling must be properly configured
in order for roll-forward recovery to be available in the event that
you need to restore the metadata server.
The SAS Metadata Server
is an “in-memory” server. As clients submit queries
and updates, the requested records are read from repository data sets
into the server's memory. When journaling is not enabled, clients
that request metadata updates must wait for updates to be written
to both the in-memory records and the repository data sets on the
file system before client access is resumed.
When journaling is enabled,
access is returned to clients as soon as the metadata updates are
written to the in-memory database and the journal file. The more time-consuming
updates to the repository data sets are performed later in the background. If
the metadata server fails before the update process has had a chance
to apply all updates from the journal file, the metadata server automatically
recovers them from the journal file when it is restarted.
The metadata server
is initially set up to write journal entries to a journal file that
is stored in the same directory as the most recent metadata server
backup. If problems occur that prevent the repository data sets from
being updated from the journal, an alert e-mail message is generated.