What is bufwaits (onstat -p)

Hello friends, What is bufwaits? Is it incremented when somebody has to access a buffer but has to wait as somebody else is accessing the buffer? I have read somewhere that bufwaits can be reduced by increasing the BUFFERS parameter in onconfig. I agree increasing BUFFERS parameter will reduce/avoid ov_buffer but I don't understand how BUFFERS parameter affects bufwaits. I think bufwaits will be affected by number of concurrent threads or cleaners or CPU VPs What do you say? Thanks in advance Vinod Bhansali ________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com

The bufwaits indicates when a thread has to wait to read a page into a buffer from disk usually this is caused by the LRU Queue to which the thread has hashed to acquire a buffer being locked by another thread trying to do the same thing or needing to move a buffer from the 'clean' part of the queue to the 'dirty' part so it can modify the page it contains. Sometimes the condition is caused by buffer flushing activities for the same reason. Another cause is the need to latch a buffer that already contains data to move it to the MRU end of the queue. Increasing BUFFERS CAN help somewhat but the most effect is obtained by increasing LRUS which reduces the probability that there will be contention for the LRU that the thread hashes to (or the ones that it rehashes to after spinning for too long). If there is still LRU contention even after maxing LRUS out (128 in 7.[123]x) there are some undocumented ONCONFIG parameters that control how a thread selects an LRU queue which can reduce contention when there are a large number of threads. But since they are undocumented save these as a last resort. If bufwaits exceeds 7% of (pagreads + bufwrits) you are probably suffering from LRU contention, if >10% you are in LRU contention HELL! Art S. Kagel Vinod Bhansali wrote: > > Hello friends, > > What is bufwaits? > Is it incremented when somebody has to access a buffer but has to wait as > somebody else is accessing the buffer? > > I have read somewhere that bufwaits can be reduced by increasing the BUFFERS > parameter in onconfig. I agree increasing BUFFERS parameter will > reduce/avoid ov_buffer but I don't understand how BUFFERS parameter affects > bufwaits. > > I think bufwaits will be affected by number of > concurrent threads or cleaners or CPU VPs > > What do you say? > > Thanks in advance > Vinod Bhansali > ________________________________________________________________________ > Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com