gc current grant 2 –way
In a 2 Node or 3 Node RAC environment when a instance needs a block in current mode, it sends the request to the master instance. The master instance finds that currently no instances, including self , has any lock on the requested block. It sends a message back to the requesting instance granting it the shared lock on the block. The requesting instance then reads the block from the disk. This event does not indicate any contention. The presence of this event in the Top 5 list indicated that the instance is spending a significant amount of time in obtaining the locks.
· Tune the SQL to optimize the number of blocks accessed by the application, thereby reducing the no of blocks it is requesting.
gc current block 2 –way
An instance requests authorization for a block to be accessed in the current mode to modify the block. The instance mastering the corresponding resource received the request. The master has the current version of the block and sends the current copy of the block to the requestor via the Cache Fusion mechanism. This event indicates write/write contention. The appearance of gc current block 2 way in the Top 5 event section does not necessarily indicate performance issues. It merely indicated that the instances are accessing copies of data present in each other’s cache and that the cache fusion mechanism is being used to transfer copies of the data among the instances. However if the average wait time for each event is very high, it might be impacting performance and needs further analysis.
· Analyze the contention. Segments in the Current Blocks Received section of the AWR report should help to identify the top contentious objects.
· Ensure the good database object design practices, database object layout, and space management practices are being followed for the top contentious objects.
In the next blog i will come out with a clear cut definitions and various types of RAC Wait Events.
No comments:
Post a Comment