On Mon, 2005-01-24 at 19:36 -0600, Min Xu (Hsu) wrote: > In any case, I think only when contention is high the non-blocking > algorithms are worth looking at. So can someone shine some light > on where the contention might be?
The major point of contention that has been identified in the past is over the BufMgrLock, which is an LWLock that protects (1) the buffer manager's lookup hash table (2) some aspects of the state of individual buffers themselves (e.g. a buffer's flags and shared refcount -- see the BufferDesc structure). Amazingly, there *are* lock-free hash table algorithms (e.g. [1]), but at first glance they seem pretty complex, and I'm not sure how much they would help (we'd still need some form of synchronization to protect access to buffer flags etc.) I think the better route to fixing this problem is just rethinking how we do locking in the bufmgr. There probably are other points of contention, but I think the BufMgrLock has been the one that has stood out in the past -- if/when that is resolved it will be easier to see what issues remain. -Neil [1] http://www.cs.rug.nl/~wim/mechver/hashtable/ ---------------------------(end of broadcast)--------------------------- TIP 7: don't forget to increase your free space map settings
