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Oracle Distributed Systems
book

Oracle Distributed Systems

by Charles Dye
April 1999
Intermediate to advanced content levelIntermediate to advanced
552 pages
15h 39m
English
O'Reilly Media, Inc.
Content preview from Oracle Distributed Systems

Snapshot Logs

Asnapshot log is a table that resides at the master site and that keeps track of changes to a master table. The name of the snapshot log table is MLOG$_master_table_name. Snapshot logs make FAST refreshes possible because the refresh process can consult the snapshot log to determine which rows have changed since the previous refresh; it then applies only these changes instead of replacing every record in the snapshot. In other words, snapshot logs enable the use of FAST refreshes. For tables with more than 100,000 records, a FAST refresh is the only viable means of maintaining a snapshot.

Note

In order for Oracle to utilize the FAST refresh mechanism, the snapshot log must be created at the master site before the snapshot itself.

Restrictions on Snapshot Logs

Pleasenote that in Oracle8, which uses primary keys to identify records in the master table, the master table must have a primary key defined and enabled in order to create a snapshot log.

Creation Tips

Records in a snapshot log are never updated, so you should create them with storage parameters that pack records as tightly as possible so you will realize the best performance and most efficient use of space.

Snapshot Logs for ROWID Snapshots

If your master table is in an Oracle8 database and the snapshot either is in an Oracle7 database or was created using the WITH ROWID option, then you must also create the snapshot log using the WITH ROWID option. Try to use primary key snapshots whenever possible because of the ...

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Publisher Resources

ISBN: 1565924320Supplemental ContentCatalog PageErrata