On 7 September 2012 00:42, aaron morton <aa...@thelastpickle.com> wrote: > 1. When a write request is received, it is written to the base CF and > secondary index to secondary (hidden) CF. If this right, will the secondary > index be written local the node or will it follow RP/OPP to write to nodes. > > it's local. > If an index is to be updated the previous column values from be read from > the primary CF so they can be deleted from the secondary index CF before > inserting the new values.
https://issues.apache.org/jira/browse/CASSANDRA-2897 (in trunk) removes that read of the previously indexed values from the update path. > > 2. When a coordinator receives a read request with say predicate x=y where > column x is the secondary index, how does the coordinator query relevant > node(s)? How does it avoid sending it to all nodes if it is locally indexed? > > When you ask for x=y the coordinator has no idea the rows for that query > exist in the cluster. If you ask at CL ONE it only does a local read. If you > ask at a higher CL it asks CL nodes for each TokenRange in the cluster. Or > for a restricted token range if you have a key restriction in the query. > > If there is any article/blog that can help understand this better, please > let me know. > > I think this is still mostly relevant > http://www.datastax.com/docs/0.7/data_model/secondary_indexes > > Cheers > > ----------------- > Aaron Morton > Freelance Developer > @aaronmorton > http://www.thelastpickle.com > > On 6/09/2012, at 5:32 PM, Venkat Rama <venkata.s.r...@gmail.com> wrote: > > Hi All, > > I am a new bee to Cassandra and trying to understand how secondary indexes > work. I have been going over the discussion on > https://issues.apache.org/jira/browse/CASSANDRA-749 about local secondary > indexes. And interesting question on > http://www.mail-archive.com/user@cassandra.apache.org/msg16966.html. The > discussion seems to assume that most common uses cases are ones with range > queries. Is this right? > > I am trying to understand the low cardinality reasoning and how the read > gets executed. I have following questions, hoping i can explain my question > well :) > > 1. When a write request is received, it is written to the base CF and > secondary index to secondary (hidden) CF. If this right, will the secondary > index be written local the node or will it follow RP/OPP to write to nodes. > 2. When a coordinator receives a read request with say predicate x=y where > column x is the secondary index, how does the coordinator query relevant > node(s)? How does it avoid sending it to all nodes if it is locally indexed? > > If there is any article/blog that can help understand this better, please > let me know. > > Thanks again in advance. > > VR > >
