Topic : Database Buffer Cache(DBC)

What are the free buffers in the database buffer cache.


  • Buffer that have changed should be pushed to the disk.
  • Buffers that are currently in use.
  • Buffer that are being written to disk.
  • Buffer that can be overwritten.

Answer :

Buffer that can be overwritten.

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What is Database Writer (DBWR) and when does DBWR write to the data file?


Answer :

- DBWR is a background process that writes data blocks information from Database buffer cache to data files.
There are 4 important situations when DBWR writes to data file
- Every 3 seconds
- Whenever checkpoint occurs
- When server proces

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What is the purpose of configuring more than one Database Writer Processes? How many should be used? (On UNIX)


Answer :

- DBWn process writes modified buffers in Database Buffer Cache to data files; so that user process can always find free buffers.
- To efficiently free the buffer cache to make it available to user processes; you can use multiple DBWn processes.
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How would you go about increasing the buffer cache hit ratio?


Answer :

Use the buffer cache advisory over a given workload and then query the v$db_cache_advice table. If a change was necessary then I would use the alter system set db_cache_size command.

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