Oracle at Work | 81
5. The HR clerk commits the transaction.
6. The Log Writer (LGWR) process writes the redo information for the entire
transaction from the redo log buffer to the current redo log file on disk. When
the operating system confirms that the write to the redo log file has successfully
completed, the transaction is considered committed.
7. The server process sends a message to the client confirming the commit.
The user could have canceled or rolled back the transaction instead of committing it,
in which case the server process would have used the old image of the employee data
in the rollback segment to undo the change to the database block.
Figure 3-8 shows the steps described here. Network traffic appears as dotted lines.
Figure 3-8. Steps for a transaction
SGA
LGWR
Datafiles Control FIles Redo Logs
Redo Log
Buffer Shared Pool Database Buffer
Cache
Client
NETWORK
6
5 Commit
7 Committed!
Redo to disk
1 Update
Server
Save undo
and update
emp name
Reuse orprocess SQL
Redo for changes
3 2 4
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Chapter 4 CHAPTER 4
Oracle Data Structures 4
In the previous chapters, we examined some distinctions between the different components
that make up an Oracle database.
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