Using Configuration Settings to Optimize Metadata Server Performance

Configuring Metadata Server Journaling

In SAS 9.2, journaling is enabled by default for the SAS 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.

For best performance, it is recommended that journaling be enabled at all times. The initial settings for journaling are as follows:

The name of the journal file is MetadataJournal.dat.
The journal file is written to the following path:

SAS-configuration-directory/Lev1/SASMeta/MetadataServer/Journal
200 megabytes of storage on the metadata server are reserved for the journal file and cannot be used for other processes.
If problems occur that prevent the repository data sets from being updated from the journal, an alert e-mail message is generated. A copy of the metadata server configuration file (omaconfig.xml) is attached to the message.

Note: For convenience and ease of management, the journal file is written by default to a subdirectory of the metadata server startup directory. To provide maximum server reliability and performance, you should consider changing the journal location to another file system. For details, see Move the Journal File to Another File System. [cautionend]

You can also change other options such as the amount of storage that is reserved for the journal file and the alert e-mail options, as described in Change the Journaling Options.

Change the Journaling Options

In SAS 9.2, journaling is enabled by default. If you need to change the initial settings, you can do so by modifying the metadata server configuration files. You can make the following types of changes:

Specify a different name or path for the journal file.

If you want to specify a different name or path for the journal file, you can change the value of the JOURNALPATH option in omaconfig.xml. For details about moving the journal file, see Move the Journal File to Another File System.

Change the alert notification settings.

The initial alert notification settings are based on values that were provided to the SAS Deployment Wizard during installation. You can change your alert notification configuration by providing different values for the following options:

ALERTEMAIL and ALERTEMAILATTACHMENT in omaconfig.xml. You can also specify ALERTEMAILTEST, which enables you to determine whether the e-mail alert options that you have specified are valid.
the EMAILSYS, EMAILHOST, and EMAILID metadata server invocation options.

Change the amount of storage on the metadata server that is allocated for the journal file.

The initial journal size of 200 MB (on 32-bit machines and z/OS systems) and 500MB (on 64-bit machines) should be sufficient for most sites. However, if clients regularly experience delays in getting their add, update, and delete requests processed, check the SAS Metadata Server log for messages similar to the following:

WARNING: insufficient file space available in journal file.

If this situation occurs, consider setting a higher value for the JOURNALSIZE option in omaconfig.xml.

Enable or disable journaling.

In SAS 9.2, journaling is enabled by default. If you want to disable journaling, then specify a blank string ("") for the JOURNALPATH option.

Note: For optimum performance, it is strongly recommended that journaling be enabled at all times. [cautionend]

For details about updating omaconfig.xml, see Reference Information for omaconfig.xml. For details about updating the metadata server invocation options, see Modifying the Metadata Server Invocation Options. After modifying the configuration files, you must restart the metadata server to enable the changes.

Move the Journal File to Another File System

For convenience and ease of management, the journal file (MetadataJournal.dat) is written by default to the following path on the metadata server machine:

SAS-configuration-directory/Lev1/SASMeta/MetadataServer/Journal

To provide maximum server reliability and performance, you should consider changing the journal location to another file system that is fast and highly reliable.

This recommendation is especially important if it is at all likely that the metadata server's file system will fill up. If the server's file system fills up, the journal file is not threatened because it is a fixed size. However, the metadata server log will need space to be able to record any disk-full messages in order to send them to the metadata server administrator.

To change the location of the journal file, follow these steps:

Create a directory for the journal. Make sure that the directory is in a file system that meets the following criteria:
- The file system should be fast and highly reliable.
- The file system should be local to the metadata server machine. Do not use a network-mounted file system or network appliance.
Make sure that the new directory has the same permissions as the previous journal location.
Open the omaconfig.xml file, and edit the JOURNALPATH parameter to point to the new location and the filename MetadataJournal.dat. For details, see Reference Information for omaconfig.xml.
Stop the metadata server.
Physically copy the journal file (MetadataJournal.dat) from its current location to the new location.
Start the metadata server.
Check the server log to make sure that no errors occurred and that the new journal location is being used.

If the log indicates that no journal file was found and that a new empty journal file was created, then you might have specified an incorrect path in the JOURNALPATH option, or you might have copied the file to an incorrect location.

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