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SQL Server transactions Architecture - October 24, 2008 at 18:10 pm
by Rajmeet Ghai
What operations do SQL Server transaction logs support?
Operations supported by transaction Logs:-
Recovery of individual transactions
In case an operation fails, a transaction can be rolled back
Recovery of all Incomplete Transactions When SQL Server Is started
In case the SQL server fails, all transactions that were in a state of
execution can be recovered. This operation helps to maintain integrity of the
database.
Rolling a Restored Database, File, File group, or Page Forward to the Point
of Failure
In case of a hardware or disk failure, if any database file is affected; it can
be restored to the point after which the failure occurred.
Supporting Transactional Replication
Transactions can be replicated from the transaction log into the distribution
database
Supporting Standby-Server Solutions
A primary server sends the active transaction log of the primary database to
one or more destinations. This destination is a standby server.
Explain the purpose of check points in a transaction log.
Checkpoints are used for backup of transactions. When a checkpoint is introduced
in a state and the next state is achieved; if something goes wrong in the new
state, the transaction can be returned to the checkpoint. This means that
checkpoints allow the transactions to be rolled back.
What is write-ahead transaction log?
A write-ahead transaction log on the disk where modifications are written first
before the associated log record is written to disk. This is to maintain the
ACID properties. Data modifications are not made to the disk directly. They are
made to the buffer cache first. Because log records are always written ahead of
the associated data pages, the log is called a write-ahead log.
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