Configuring Metadata Server Journaling

About Metadata Server Journaling

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.

About the Journal Options

Journaling is controlled by options that are set in the omaconfig.xml file when you install or migrate your system. In most cases, there is no need to change the initial settings.
The OMA JOURNALTYPE option specifies the type of journal file that is created. By default, the SAS Deployment Wizard sets the value of this option to ROLL_FORWARD, which creates a linear journal file that permanently stores all transactions that have occurred since the most recent backup. The journal file is written to the same location as the associated backup files. Each time a new backup is executed, journaling stops and a new journal file is started in the new backup location.
ROLL_FORWARD must be specified if you want to be able to use roll-forward recovery in the event of a metadata server failure.
Other allowable values for OMA JOURNALTYPE are SINGLE and NONE. These values are not recommended. If you specify one of these values, then roll-forward recovery is not available.
Additional options in omaconfig.xml that apply to journaling include the following:
  • JOURNALSIZE and JOURNALPATH, which are applicable only if you specify SINGLE as the OMAJOURNALTYPE.
  • JOURNALYIELDCOUNT, which specifies the number of records that the update process can apply before yielding to allow other internal processing tasks. Do not change this setting without consulting with SAS Technical Support.