some suggestions for rac performance

1. If possible, please use CACHE + NOORDER for sequences on RAC:
This setting has the least performance impact on RAC, and it is the default when creating a new sequence wihtout options. Each instances caches a distinct set of numbers in the shared pool. Sequences will not be globally ordered, and gaps will occur when the shared pool is refreshed (e.g. instance shut down) like on single instance databases.

Please refer below note for details:
RAC and Sequences (Doc ID 853652.1)

2. Using table/index partitioning to reduce inter-instance contention.
o Range or list partitioning may be very effective in conjunction with data dependent routing, if the workload can be directed to modules from a particular instance.
o Hash partitioning may help to reduce buffer busy contention by making buffer access distribution patterns sparser, allowing more buffers to be available for concurrent access

3. Configure network settings at the OS to reduce 'gc cr multi block request' waits. See your OS specific documentation for instructions on how
to do this. If using UDP, make sure the parameters relating to send buffer space, receive buffer space, send highwater, and receive highwater are set well above the OS default. The alert.log will indicate what protocol is being used.

Example:

Sun (UDP Protcol)
UDP related OS parameters can be queried with the following command:
ndd /dev/udp udp_xmit_hiwat
ndd /dev/udp udp_recv_hiwat
ndd /dev/udp udp_max_buf
Set the udp_xmit_hiwat and udp_recv_hiwat to the OS maximum with:
ndd -set /dev/udp udp_xmit_hiwat
ndd -set /dev/udp udp_recv_hiwat
ndd -set /dev/udp udp_max_buf <1M or higher>

4. Using Parallel Instance Groups

If you want to limit the parallel execution within one instance or a group of instances, you should establish the group membership by setting the INSTANCE_GROUPS and the PARALLEL_INSTANCE_GROUP init.ora parameters.

5. The use of locally managed tablespaces (instead of dictionary managed) with
the 'SEGMENT SPACE MANAGEMENT AUTO' option can reduce dictionary and freelist
block contention.

See below note for details:
Tuning Inter-Instance Performance in RAC and OPS (Doc ID 181489.1)

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