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Question and Answer

Chris Saxon

Thanks for the question, Prakash.

Asked: October 05, 2015 - 1:42 pm UTC

Last updated: October 06, 2015 - 12:34 pm UTC

Version: 12.1.0.2

Viewed 1000+ times

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Formula to set PARALLEL_MAX_SERVERS
---------------------------------------------------------
PARALLEL_MAX_SERVERS = PARALLEL_THREADS_PER_CPU * CPU_COUNT * concurrent_parallel_users * 5

If AMM is disabled, the value of concurrent_parallel_users is 1.

If only PGA AMM is enabled, then the value of concurrent_parallel_users is 2.

If both SGA and PGA AMM is enabled, then the value of concurrent_parallel_users is 4.

Starting with 11gR2, the value of PARALLEL_MAX_SERVERS cannot be greater than (PROCESSES -15) as per note “How PARALLEL_MAX_SERVERS and PROCESSES Parameters are Related? (Doc ID 1968840.1)”

So in our case,

PARALLEL_MAX_SERVERS = 2 * 64 * 4 * 5 = 2560, however PROCESSES is 1000…so the value of PARALLEL_MAX_SERVERS should have been 985 as per the formula mentioned in the (Doc ID 1968840.1).

However, I see this in the alert log:

Adjusting the default value of parameter parallel_max_servers
from 2560 to 826 due to the value of parameter processes (1000)


Not sure how this value 826 is calculated, so please help me to understand how this value 826 is been calculated?


and Chris said...

I got in touch with Yasin Baskan, the PM for parallel regarding this. He had this to say:

That note seems to be wrong. The default value for PARALLEL_MAX_SERVERS is calculated as described in the doc. We also calculate (PROCESSES - no_of_reserved_processes) and PARALLEL_MAX_SERVERS is set to the minimum of these two values.

The number of reserved processes depend on the version and on the platform. So, 15 is not a fixed number. In your case the database reserves 174 processes and the rest goes to PARALLEL_MAX_SERVERS.

The number of reserved processes is calculated by the VOS layer.


The note will be corrected in due course.

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