Simpler Navigation for Servers and Operating Systems - Please Update Your Bookmarks
Completed: a much simpler Servers and Operating Systems section of the Community. We combined many of the older boards, so you won't have to click through so many levels to get at the information you need. Check the consolidated boards here as many sub-forums are now single boards.
If you have bookmarked forums or discussion boards in Servers and Operating Systems, we suggest you check and update them as needed.
Showing results for 
Search instead for 
Did you mean: 

db_writer_processes and dbwr_io_slaves process


db_writer_processes and dbwr_io_slaves process


I am not able to find a official Oracle doc which tells the rule to decide, which parameter to use between dbwr_io_slaves and db_writer_processes based on the number of CPUs available on the system.

Could somebody please help ?

Best Regards
Volker Borowski
Honored Contributor

Re: db_writer_processes and dbwr_io_slaves process


as far as I remember:

dbwr_io_slaves is fairly out-dated due to running the systems with async IO. This was a way to provide something similar as async IO without having this feature in the OS.

With async IO you should be ok with a single db_writer an no io_slaves. If you have a large db_cache and/or lots of CPU increasing DB_WRITER_PROCESSES will provide better checkpoint performance.

I currently support a DB with 60 CPUs and 85GB db_cache_size (on AIX) and without setting db_wr_processes it defaulted to 8
in this case.

No official statement so far, but as you see, oracle itself has a rule to increase this if resources are sufficiant. I assume it calculates it utilizing db_cache_size and cpu_count and depends on async IO being configured in the OS kernel.