Thanks Tyler for the details. I'm still trying to understand what you described.
Just to simplify my question & what I don't understand: When coordinator fires indexed scan request to node 192.168.51.22, why don't it ask that node to check all of its (at least primary) ranges for the queried data, at once. Also, internally that node should be able to just do one scan through all of the ranges held by it, isn't it? (e.g. [min(-9223372036854775808), max(-9193352069377957523), and (max(-9136021049555745100), max(-8959555493872108621)], etc. ] Seems like it needs to query data in token order. So, min(-9223372036854775808), max(-*9193352069377957523*) on 192.168.51.22. But next range ((max(-*9193352069377957523*), max(-*9136021049555745100*)]) is on 192.168.51.25 so fire query there. Then, next range (max(- *9136021049555745100*), max(-8959555493872108621)] again on 192.168.51.22. Btw,, I'm not too sure regarding min/max or max/max in trace output. I found below comment in https://issues.apache.org/jira/browse/CASSANDRA-4858. "The problem is that we have to scan the nodes in token order so we dont break the existing API's, if we do so then we are sending a lot more requests and waiting for the response than the number of nodes. " Don't understand the restriction though - "don't break the existing API's". With non-vnode, it only queries a particular node only one time..Btw, in the worst case, I understand secondary index query has to scan all the nodes in cluster sometime (empty table or high cardinality index?) but I don't understand why vnode makes it to scan the *same node *multiple times. If RF is 1, then also I see this behavior. >> Snippet from output1.txt attached earlier: Executing indexed scan for [min(-9223372036854775808), max(-9193352069377957523)] | 23:11:30,992 | 192.168.51.22 | Executing indexed scan for (max(-9193352069377957523), max(-9136021049555745100)] | 23:11:30,998 | 192.168.51.25 | Executing indexed scan for (max(-9136021049555745100), max(-8959555493872108621)] | 23:11:30,999 | 192.168.51.22 | Executing indexed scan for (max(-8959555493872108621), max(-8929774302283364912)] | 23:11:31,000 | 192.168.51.25 | Great if you or someone can describe further. Thanks!! On Fri, Sep 19, 2014 at 2:33 PM, Tyler Hobbs <ty...@datastax.com> wrote: > > On Fri, Sep 19, 2014 at 4:19 PM, DuyHai Doan <doanduy...@gmail.com> wrote: > >> >> But does it implies that with vnodes, there are actually "extra work" to >> do for scanning indices ? >> > > Yes. > > >> If yes, is this "extra load" rather I/O bound or CPU bound ? >> > > It doesn't necessarily change what the query is "bound" by, except perhaps > in the case where you have almost no matching results. There are more > messages to dispatch and handle. > > > -- > Tyler Hobbs > DataStax <http://datastax.com/> >
