This wait event usually occurs when you have tried to dynamically resize a component of the SGA such as the buffer cache.
The "buffer exterminate" waits can only happen if part of the buffer cache is being dynamically shrunk and a session wants access to a data block that resides in a db cache buffer within a granule chosen to be freed. After the buffer is freed (removed from buffer cache hash chain, LRU chain, etc.), one of the waiting sessions can then reload that block into one of the remaining db cache granules, and everyone else eventually finds the new buffer address for the data block via hash lookup.
You can check the following views to see if any recent SGA Component resize operations have taken place :
V$SGA_DYNAMIC_COMPONENTS displays information about the dynamic SGA components. This view summarizes information based on all completed SGA resize operations since instance startup.
V$SGA_CURRENT_RESIZE_OPS displays information about SGA resize operations which are currently in progress. An operation can be a grow or a shrink of a dynamic SGA component.
V$SGA_DYNAMIC_FREE_MEMORY displays information about the amount of SGA memory available for future dynamic SGA resize operations.
来自 “ ITPUB博客 ” ，链接：http://blog.itpub.net/15747463/viewspace-774920/，如需转载，请注明出处，否则将追究法律责任。