> This is my understanding from using cassandra for probably around 2 years Sounds about right.
Cheers ----------------- Aaron Morton Freelance Cassandra Developer New Zealand @aaronmorton http://www.thelastpickle.com On 26/02/2013, at 7:43 AM, "Hiller, Dean" <dean.hil...@nrel.gov> wrote: > This is my understanding from using cassandra for probably around 2 > years….(though I still make mistakes sometimes)…. > > For CL.ONE read > > Depending on the client, the client may go through one of it's known > nodes(co-ordinating node) which goes to real node(clients like > astyanax/hector read in the ring information and usually go direct so for > CL_ONE, no co-ordination really needed). The node it finally gets to may not > have the data yet and will return no row while the other 2 node might have > data. > > For CL.QUOROM read and RF=3 > Client goes to the node with data(again depending on client) and that node > sends off a request to one of the other 2. Let's say A does not have row > yet, but B has row, comparison results and latest wins and a repair for that > row is kicked off to get all nodes in sync of that row. > > If local node responsible for key replied that it have no data for this key - > will coordinator send digest commands? > > IT looks like CL_ONE does trigger a read repair according to this doc (found > googling CL_ONE read repair cassandra) > > http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/CL-ONE-reads-RR-badness-threshold-interaction-td6247418.html > > http://wiki.apache.org/cassandra/ReadRepair > > Later, > Dean > > Explain please, how this work when I request for key which is not in database > > > * The closest node (as determined by proximity sorting as described above) > will be sent a command to perform an actual data read (i.e., return data to > the co-ordinating node). > * As required by consistency level, additional nodes may be sent digest > commands, asking them to perform the read locally but send back the digest > only. > * For example, at replication factor 3 a read at consistency level > QUORUM would require one digest read in additional to the data read sent to > the closest node. (See > ReadCallback<http://wiki.apache.org/cassandra/ReadCallback>, instantiated by > StorageProxy<http://wiki.apache.org/cassandra/StorageProxy>) > > I have multi-DC with NetworkTopologyStrategy and RF:1 per datacenter, and > reads are at consitency level ONE. If local node responsible for key replied > that it have no data for this key - will coordinator send digest commands? > > Thanks!
