Wait events in Oracle RAC

Oracle RAC (11g / 12c) wait events

In Oracle 9i and prior, the "gc" was spelled out as "global cache" in the RAC wait events.

In RAC wait event names, CR stands for Consistent Read.
Current - is for DMLs
CR - is for Selects
The difference between CR and Current is that CR requires a block with a given SCN, whereas current does not (current mode fetches the block with the current SCN).

gc buffer busy release =>  specifies the time the remote instance locally spends accessing the requested data block. Caused may be because of not enough memory on your nodes, overloaded interconnect.
gc buffer busy acquire

gc current request 
gc cr request => the time it takes to retrieve the data from the remote cache. Oracle may not pick private interconnect and instead route traffic over slower public network. RAC event similar to buffer busy waits, tune SQL to request less data, tune network latency between RAC nodes, localize data access.

gc cr failure 
gc current block lost => Lost blocks due to Interconnect or CPU. Indicates interconnect issues and contention.
gc cr block lost => Lost blocks due to Interconnect or CPU. Indicates interconnect issues and contention.
gc current block corrupt
gc cr block corrupt

gc current block busy => The current block read request was delayed, most likely an I/O bottleneck. Block is already involved in GC operation, shows hot blocks or congestion.
gc cr block busy => The consistent read request was delayed, most likely an I/O bottleneck. Blocks are busy in another instance, check for block level contention or hot blocks.
gc current block congested => Long run queues and/or paging due to memory deficiency. Current block congestion, check for hot blocks or busy interconnect.
gc cr block congested => Long run queues and/or paging due to memory deficiency. cr block congestion, check for hot blocks or busy interconnect.

gc current block 2-way   => Blocks are busy in another instance, check for block level contention or hot blocks.
gc cr block 2-way => Blocks are busy in another instance, check for block level contention or hot blocks.
gc current block 3-way => Blocks are busy in another instance, check for block level contention or hot blocks.
gc cr block 3-way => Blocks are busy in another instance, check for block level contention or hot blocks.

gc current grant 2-way
gc cr grant 2-way
gc current grant busy
gc current grant congested
gc cr grant congested

gc cr multi block read
gc current multi block request => Full table or index scans.
gc cr multi block request => Full table or index scans.
gc cr block build time
gc current block flush time
gc cr block flush time
gc current block send time
gc cr block send time
gc current block pin time
gc domain validation 
gc current retry
ges inquiry response
gcs log flush sync

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