Parallelism with number of CPUs

[sivakumarocp]

Hi Tim,

I am donig cross platform migraion, for that i need to migrate tablespaces from solaris to linux host. I thought of using PARALLELISM option along with convert tablespace RMAN command but I am bit confused on how much value that i can give for parallelism parameter in RMAN.

in my solaris has 4 physical CPUs with 32G memory.

Code: Select all

oracle:orprod96@admin-vsr256 /oracle > psrinfo
0       on-line   since 09/06/2011 13:52:40
1       on-line   since 09/06/2011 13:52:40
2       on-line   since 09/06/2011 13:52:40
3       on-line   since 09/06/2011 13:52:38

in this case, while doing actual conversion how much value that i can give at the maximum for PARALLELISM parameter in RMAN.

Only one database is running on this host.

[Tim...]

Hi.

The answer as always is, it depends.

- If the process is waiting on CPU mostly, then it is pointless using more than one slave per available core or they are just holding each other up.
- If the process is waiting predominantly on factors other than CPU, then adding more slaves that cores is fine from a CPU perspective.
- Parallelism only works if none of the factors affecting it (CPU, memory, network, disk) are bottlenecked. As soon as one or more factors are maxed out, adding more slaves actually reduces performance as it is adding to the bottleneck.

Cheers

Tim...