Page 155 - DCAP508_DATABASE_ADMINISTRATION

Unit 10: Database Backup and Restore

depending on your disk resources. Then, each time a new snapshot is created, the earliest Notes
snapshot can be deleted.

To recover from a user error, you can revert the database to the snapshot immediately
before the error. Reverting is potentially much faster for this purpose than restoring
from a backup; however, you cannot roll forward afterward.

Alternatively, you may be able to manually reconstruct a dropped table or other
lost data from the information in a snapshot. For instance, you could bulk copy the
data out of the snapshot into the database and manually merge the data back into the
database.

Notes Your reasons for using database snapshots determine how many concurrent
snapshots you need on a database, how frequently to create a new snapshot, and how long
to keep it.

Managing a test database
In a testing environment, it can be useful when repeatedly running a test protocol for the
database to contain identical data at the start of each round of testing. Before running the
first round, an application developer or tester can create a database snapshot on the test
database. After each test run, the database can be quickly returned to its prior state by
reverting the database snapshot.

10.4.7 Limitations and Requirements of Database Snapshots

A database snapshot captures the point in time at which snapshot creation began, minus any
uncommitted transactions. Before using database snapshots, you should understand the impact
of database snapshots on the source database and the system environment, as well as limitations
on the snapshots themselves.

Limitations on the Source Database

As long as a database snapshot exists, the following limitations exist on the snapshot’s source
database:
The database cannot be dropped, detached, or restored.

Notes Backing up the source database works normally; it is unaffected by database
snapshots.
Performance is reduced, due to increased I/O on the source database resulting from a
copy-on-write operation to the snapshot every time a page is updated.

Files cannot be dropped from the source database or from any snapshots.
The source database must be online, unless the database is a mirror database within a
database mirroring session.

Notes All recovery models support database snapshots.

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