as a administrator, I want to know why I can read the data from any node, because the data just be kept the replica. Can you tell me? Thanks in advance.
-----Original Message----- From: Edward Capriolo [mailto:edlinuxg...@gmail.com] Sent: Friday, January 14, 2011 9:44 AM To: user@cassandra.apache.org Subject: Re: about the data directory On Thu, Jan 13, 2011 at 7:56 PM, raoyixuan (Shandy) <raoyix...@huawei.com> wrote: > I have some confused, why do the users can read the data in all nodes? I mean > the data just be kept in the replica, how to achieve it? > > -----Original Message----- > From: sc...@scode.org [mailto:sc...@scode.org] On Behalf Of Peter Schuller > Sent: Friday, January 14, 2011 1:19 AM > To: user@cassandra.apache.org > Subject: Re: about the data directory > >> So you mean just the replica node 's sstable will be changed ,right? > > The data will only be written to the nodes that are part of the > replica set fo the row (with the exception of hinted handoff, but > that's a different sstable). > >> If all the replica node broke down, whether the users can read the data? > > If *all* nodes in the replica set for a particular row are down, then > you won't be able to read that row, no. > > -- > / Peter Schuller > It does not matter which node you connect to. The node you connect to determines the hash of the key (or uses the key itself when using Order Preserving Partitioner) to determine which node or nodes the data should be on. If the key is on that node it returns it directly to the client. If the key is not on that node Cassandra fetches it from another node and then returns that data. The client is unaware and does not need to be concerned with where the data came from.
