On Fri, Sep 19, 2014 at 4:53 PM, Jay Patel <pateljay3...@gmail.com> wrote:
> > 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. > The coordinator certainly could batch multiple range requests that are going to the same replica. It's an optimization that would primarily help the empty table/high cardinality case, but you're welcome to open a ticket. 3.0 is the earliest this would make it in. > > 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". > I think he's just saying that we have to make sure we return results in token order (and if there's a limit on the query, return the first N results when listed in token order). > > 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 | > I'm not sure how your question here is different from the one above. -- Tyler Hobbs DataStax <http://datastax.com/>
