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02-25-2009 01:02 AM
02-25-2009 01:02 AM
db_writer_processes and dbwr_io_slaves process
Hi,
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
Sudhir
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
Sudhir
1 REPLY 1
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02-28-2009 05:39 AM
02-28-2009 05:39 AM
Re: db_writer_processes and dbwr_io_slaves process
Hi,
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.
Volker
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.
Volker
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