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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.