WAIT EVENTS

Detection / Contention and Solution:

DB File Scattered Read

DB File Sequential Read

Read By Other Session / Buffer busy wait / Segment buffer busy wait / Block Contention

Free Buffer Wait

Log file sync

Log file parallel write

Log File Switch

Log Buffer Space

Direct Path Writes

Direct Path Reads

Shared pool latch

Library cache latch

Latch Free Waits

Cache Buffer LRU Chain Latch

Cache Buffer Chain Latch

Enqueue Wait

Row cache objects latch

Idle Event

RDBMS IPC Message

Row Lock Contention

Index Leaf Block Contention


RAC : Wait Events

current read block - locally instance read block
cr block - consistent read block

• Block Oriented Wait  

                  gc current block 2-way

                  gc current block 3-way

                  gc cr block 2-way

                  gc cr block 3-way

• Message Oriented Wait 

                  gc current grant 2-way

                  gc current grant 3-way

                  gc cr grant 2-way

                  gc cr grant 3-way (Normally this wait event is not possible, but "_cr_grant_local_role" => turn 3-way CR grants off, make it automatic, or turn it on) 

• Contention Oriented Wait 

                  gc current block busy (cluster cache contention)

                  gc cr block busy

                  gc current buffer busy (local cache contention)

                  gc cr buffer busy (Remote cache contention)

• Load Oriented Wait  

                  gc current block congested

                  gc cr block congested

                  gc current grant congested

                  gc cr grant congested

OTHERS:

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 multi block request : Full table or index scans.

gc cr multi block request : Full table or index scans.

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 current/cr failure/retry : A block is requested and a failure status received or some other
                                            exceptional event has occured.

Reference :

ID 1911398.1 - LMS & CPU issue.