The global cache service (LMSn) processes copy consistent copies of blocks in the buffer cache to the requesting instance’s foregound process.
LMS also performs a rollback on uncommitted transactions in the requested block.
The number of LMS processes is 2, unless otherwise specified. This number is not sufficient for RAC databases with heavy transaction.
Because it is not sufficient, “gc current block 2-way” or “gc current block 3-way” wait events can be seen in the database.
The number of LMS processes is managed by the parameter GCS_SERVER_PROCESSES. The default value is 2 and the maximum value is 36. By increasing the value of this parameter, you can avoid wait events such as “gc current block 2-way”.
At the same time, block requests between intances in RAC databases can be completed in less time. This means serious performance gain.
Change the parameter:
SQL> alter system set GCS_SERVER_PROCESSES=10 scope=spfile sid='*';
The database must be restarted after the parameter change.