SAP 15 Sybase ASE Automatic Recovery | SAP ASE Recovery

Описание: Tracking Database Changes
Automatic Recovery
Checkpoints
Setting the Recovery Interval
Automatic Checkpoint Procedure
Truncating the Log After Automatic Checkpoints
Fast Recovery
SAP ASE Start-up Sequence
Bringing Engines Back Online
Parallel Recovery
Database Recovery
Specifying the Recovery Order
Changing or Deleting the Recovery Position
Listing the User-Assigned Recovery Order
Parallel Checkpoints
Recovery State
Tuning for Fast Recovery
SAP ASE uses transactions to keep track of all database changes. A transaction consists of one or more Transact-SQL statements that succeed—or fail—as a unit.
Each SQL statement that modifies data is considered a transaction. Users can also define transactions by enclosing a series of statements within a begin transaction...end transaction block.
Each database has its own transaction log, in the system table syslogs. You cannot turn off transaction logging.

The transaction log is a write-ahead log. When a user issues a statement that modifies the database, SAP ASE writes the changes to the log.
After all changes for a statement have been recorded in the log, they are written to an in-cache copy of the data page.
If any statement in a transaction fails to complete, SAP ASE reverses all changes made by the transaction. SAP ASE writes an “end transaction” record to the log at the end of each transaction, recording the status of the transaction.

Each time you restart SAP ASE, it automatically performs a set of recovery procedures on each database.
The recovery mechanism compares each database to its transaction log. If the log record for a particular change is more recent than the data page, the recovery mechanism reapplies the change from the transaction log.
If a transaction was ongoing at the time of the failure, the recovery mechanism reverses all changes that were made by the transaction.

Recovers master.
Recovers sybsystemprocs.
Recovers model.
Creates tempdb (by copying model).
Recovers sybsystemdb.
Recovers sybsecurity.
Recovers user databases, in order by sysdatabases.dbid, or according to the order specified by sp_dbrecovery_order.
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