gc current block 2-way

gc current block 2-way (write/write with 2 nodes)


Definition

- requesting instance request any data block for dml(current) from Master.
- If master is the holder of that data block and also has already modified that block.
- Then master will retain PI block for itself.
- Master will also flush respective redo log to log file before sending CURRENT block to requesting instance.
- Meanwhile requesting instance will wait in "GC CURRENT BLOCK 2-WAY"

Reason

As you know before sending the current data block to the requesting instance master instance first flush respective redo log of the log file then it will prepare PI block and then  send CURRENT block to the requesting instance over the interconnect.

- This wait event appears in "TOP-5" timed events section of AWR Report.
- Analyze the contention using AWR REPORT.
- In AWR REPORT, analyze "Current Block Recieved" and identify the top contentious objects.
- You are getting contention at segment level because of bad database design, DB object layout and Space Management.
- LGWR is not efficient to write in redo log file and thats why requesting instance is waiting in "gc current block 2-way".
- Interconnect is having N/W latency.
- Application Segregation is also a reason.

Troubleshooting

- Best Solution is to apply application Segregation means try to locate all select query on one node and all DML on another node.
- Tune LGWR
- Tune Interconnect
- Make Sure the system has enough CPU power.