On Fri, Mar 20, 2009 at 6:48 PM, Orlando Andico <[email protected]> wrote: > Oracle is not exactly shared-everything. While the storage is indeed a > single point of bottleneck, the existence of Cache Fusion means that > you will not bottleneck the disk right away.
oracle rac belongs to shared-everything architecture... the cache fusion is a global cache (distributed caching) similar to disk cache in a single node to delay writes... still a bottleneck when you are running out of memory as it needs to write to give room for incoming data to write when write load increases and you are having a scalability problem there... > As for lock contention... that's why in a correctly-configured RAC > environment you MUST use the Partitioning option as well (that's an > additional $10K+ / CPU, ka-ching!) and partition your tables properly > so that you won't have lock contention. no matter how you spend more money to improve lock contention.. there is always a lock contention in a shared-everything architecture simply because two or more nodes can still access the same block on that partition.. > To simply say "in real implementatons RAC shows negative scalability" > is a very common misconception and indeed, people see this in practice > but it's because they don't know how to tune RAC. naahhh... the internal communication of RAC in a separate channel simply shows a negative scalability when the nodes increases due to the fact that each node must coordinate with each other regarding to lock ownership and all nodes updates the same control file as well as data-block ownership transfer which creates a big bottleneck in the performance.. > Shared-nothing is very challenging simply because you don't have a > single system view. you do... > Most people don't have to have to aggregate their > data from all over the place just to do a single query. let the index do its job (if a query has a condition) and fetch those data where it resides to a particular node.. thus less load to every disk storage on every node and much faster to get the data if you compare that to a shared storage... that is why google is too damn fast to return a search query because of a shared-nothing architecture... > In any case, in Oracle 11g the new Exadata storage cell concept allows > linear scalability to very many nodes and removes the shared-storage > requirement that RAC has (traditionally) had. exadata storage cell concept scales simply because they move their traditional shared-everything storage like rac to shared-nothing like exadata storage.. your exadata storage is a shared-nothing architecture... now as you can see oracle starting to understand and reliaze how shared-nothing architecture scales... fooler. _________________________________________________ Philippine Linux Users' Group (PLUG) Mailing List http://lists.linux.org.ph/mailman/listinfo/plug Searchable Archives: http://archives.free.net.ph
