【等待時間】asynch descriptor resize

renjixinchina發表於2013-10-08
Wait event 'asynch descriptor resize' is waited for when the number of asynchronous descriptors reserved inside the OS kernel is being re-adjusted.

When the number of asynchronous I/O's submitted by a process has to be dynamically increased, the unix kernel is signalled to make the changes and the process will wait on 'asynch descriptor resize' . Many Unix Kernels (for example: Linux kernel) do not allow the limit to be increased when there are outstanding I/O's; all outstanding I/O's must be resolved before the limit is increased. This means that all sessions doing asynchronous I/O will wait at this time. The event is shown when the kernel wants to increase the limit and is waiting for all the outstanding I/O's to be resolved so that the increase can be implemented. 

If you see this wait event often, it might be a good idea to install the fix for (unpublished)  ASYNC DESCRIPTOR RESIZE which adjusts the frequency of resize calls.  
The fix for (unpublished) Bug 9829397 is included in 11.2.0.2.5, 11.2.0.3 and Oracle 12g

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