Oracle Database Tips by Donald Burleson

Snapshot Usage

Source 7.5 shows the use of the CREATE SNAPSHOT command for a simple snapshot. It is followed directly by Source 7.6, which shows use of the CREATE SNAPSHOT command with a complex snapshot. The sizing considerations should mirror those for the source table. If the source table is stable, a large initial extent with smaller subsequent extents should be used. Since snapshots will most likely be on slow-growth tables, set pctincrease to 0 in most cases.

SOURCE 7.5  Example of the CREATE SNAPSHOT command for a simple snapshot.

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In the snapshot in Source 7.5, the entire test_drugs table is used to create a snapshot from its location at a remote database identified in the kcgc connect string into the tablespace clinical_tests in the current database. It will first be refreshed in seven days at 2:00 o'clock in the morning and subsequently at seven-day intervals on every Tuesday thereafter at 2:00 o'clock in the morning. Since no refresh mode is specified, if the table has a snapshot log, the fast mode will be used since it is a simple snapshot. If no snapshot log is available, then the complete mode will be used. If you specify the FORCE option, it will always try to do a FAST refresh first.

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