Database Writer Process (DBW)

The database writer process (DBW) writes the contents of database buffers to data files. DBW processes write modified buffers in the database buffer cache to disk.

Although one database writer process (DBW0) is adequate for most systems, you can configure additional processes—DBW1-DBW9, DBWa-DBWz and BW36-BW99—to improve write performance if your system modifies data heavily. These additional DBW processes are not useful on uniprocessor systems.

The DBW process writes dirty buffers to disk under the following conditions:

  • When a server process cannot find a clean reusable buffer after scanning a threshold number of buffers, it signals DBW to write. DBW writes dirty buffers to disk asynchronously if possible while performing other processing.
  • DBW periodically writes buffers to advance the checkpoint, which is the position in the redo thread from which instance recovery begins. The log position of the checkpoint is determined by the oldest dirty buffer in the buffer cache.

 

By default there is 1 database writer process available for each database :

We can increase no of writer process using db_writer_processes parameter .

we can see it have default value 1. Now , lets change it to 3

It’s a static parameter and database must be restarted to take effect of this parameter.

This is a test database so I can use startup force else we need to gracefully shut down database and start it.

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