+1 to what AlexR said. I think there is indeed a bad assumption that shards just forward data to the coordinating node, this is not the case.
On Thu, Dec 18, 2014 at 1:09 AM, AlexR <[email protected]> wrote: > > if you take a terms aggregation, the heavy lifting of the aggregation is > done on each node then aggregated results are combined on the master node. > So if you have thousands of nodes and very high cardinality nested aggs the > merging part may become a bottleneck but cost of doing actual aggregation > in most cases is far higher than cost of merging results from reasonable > number of shards. So in practice I think it balances pretty well. Of course > you are not limited to one master to handle concurrent requests > > On Wednesday, December 17, 2014 4:12:44 PM UTC-5, Yifan Wang wrote: >> >> I thought ES only "Collect" on individual shards, and "Reduce" on Client >> Node (master if you call it), nothing is done at the data node level. >> >> On Tuesday, December 16, 2014 1:31:30 PM UTC-5, AlexR wrote: >>> >>> ES already doing aggregations on each node. it is not like it is >>> shipping row level query data back to master for aggregation. >>> In fact, one unpleasant effect of it is that aggregation results are not >>> guaranteed to be precise due to distributed nature of the aggregation for >>> multibucket aggs ordered by count such as terms >> >> -- > You received this message because you are subscribed to the Google Groups > "elasticsearch" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/elasticsearch/61122d28-8f62-4ee2-b9e7-6fd99048ee8e%40googlegroups.com > <https://groups.google.com/d/msgid/elasticsearch/61122d28-8f62-4ee2-b9e7-6fd99048ee8e%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > For more options, visit https://groups.google.com/d/optout. > -- Adrien Grand -- You received this message because you are subscribed to the Google Groups "elasticsearch" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/elasticsearch/CAL6Z4j5vQV5BsszRgrBMWiUTd9HsnWyTauTMqObCiiaFUHGFjA%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
