1Z0-052 · Question #79
Which two statements about the background process of the database writer are true? (Choose two.)
The correct answer is A. It is possible to have multiple database writers in an Oracle instance. B. It writes dirty buffers, if any, to data files whenever a checkpoint occurs. The Database Writer process (DBWn) writes modified (dirty) buffer cache blocks to data files and can be configured with multiple instances to improve write throughput.
Question
Which two statements about the background process of the database writer are true? (Choose two.)
Options
- AIt is possible to have multiple database writers in an Oracle instance.
- BIt writes dirty buffers, if any, to data files whenever a checkpoint occurs.
- CIt writes dirty buffers, if any, to data files whenever a transaction commits.
- DIt writes dirty buffers, if any, to data files before the log writer (LGWR) writes.
How the community answered
(61 responses)- A90% (55)
- C7% (4)
- D3% (2)
Why each option
The Database Writer process (DBWn) writes modified (dirty) buffer cache blocks to data files and can be configured with multiple instances to improve write throughput.
Oracle allows up to 100 database writer processes (DBW0 through DBW9 and DBWa onward) configured via the DB_WRITER_PROCESSES initialization parameter, enabling parallel writes to data files for high-throughput systems.
A checkpoint is one of the primary triggers for DBWn to flush dirty buffers from the buffer cache to data files, ensuring the data files are consistent up to the checkpoint SCN.
DBWn does not write dirty buffers on every transaction commit - that is an asynchronous process; LGWR writes the redo log entries synchronously at commit to ensure durability.
Oracle's write-ahead logging protocol requires that LGWR always writes redo log entries before DBWn writes the corresponding data blocks to data files, not the other way around.
Concept tested: Oracle DBWn background process triggers and scalability
Source: https://docs.oracle.com/cd/E11882_01/server.112/e40540/process.htm#CNCPT1247
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