Oracle7 Server Distributed Systems Volume II: Replicated Data

Offline Instantiation

Offline instantiation of a snapshot site is primarily useful for those sites with a very large amount of snapshot data where the time required to transfer the data through network links to the new site would be prohibitive.

Creating a snapshot site using offline instantiation requires that you first create a snapshot for each table in a new snapshot replication group at the master site, then do an export of the base tables to a file or files that can then be transported (via tape or another medium) to the new site and used to instantiate the new snapshot site.

Perform the following steps at the specified sites:

Master Site:

It is recommended that you create a snapshot log for each master site before instantiating the new snapshot. You must also be the owner of the schema at the master site from which the snapshots will be derived.

Create a snapshot for each of the tables in the same schema as the master schema, but give the snapshot a name that is different from the corresponding master table. You must also include the database link from the snapshot site to the master site. For example:

CREATE SNAPSHOT FOOITEM AS SELECT * FROM ioug1.item@dbs1

would work, but

CREATE SNAPSHOT FOOITEM AS SELECT * FROM ioug1.ITEM

would fail. Attention: Before creating your snapshots, ensure that you have the necessary storage space available at the master site.

As schema owner, use the Export utility to export the snapshots' base tables (those prefixed with SNAP$_). The export file(s) can then be transported to the new snapshot site.

New Snapshot Site:

Mount the tape containing the export file.

Use the procedure CREATE_SNAPSHOT_REPGROUP (gname, master_site) to create the replicated object group for the snapshot that you plan to import from the master site. Note that a replicated snapshot group must have the same name as the object group at the master site.

For each schema and snapshot, use the procedure DBMS_OFFLINE_SNAPSHOT.BEGIN_LOAD (gname, sname, snapshot_oname, master_site) to create empty snapshots in the specified schema and object group, as well as all the necessary supporting objects.

You can now import the base tables from the Export file(s).

When the import is complete, for each schema and snapshot, use the procedure DBMS_OFFLINE_SNAPSHOT.END_LOAD (gname, sname, snapshot_oname).

Master Site:

Use the DROP SNAPSHOT statement to drop the snapshots at the master site that were created for offline instantiation.

For more information about using the Import/Export utilities, see

and Oracle7 Server Utilities.