# Query response time does NOT improve by adding additional nodes **URL:** \ **Category:** Elasticsearch\ **Created:** [March 24, 2014, 8:54am UTC](https://discuss.elastic.co/t/query-response-time-does-not-improve-by-adding-additional-nodes/16557 "2014-03-24T08:54:32Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Herbert\_Bodner](https://avatars.discourse-cdn.com/v4/letter/h/a4c791/32.png) [@Herbert\_Bodner](https://discuss.elastic.co/u/Herbert_Bodner)\ **Post date:** [March 24, 2014, 8:54am UTC](https://discuss.elastic.co/t/query-response-time-does-not-improve-by-adding-additional-nodes/16557/1 "2014-03-24T08:54:32Z")
For my thesis I am going to test the scalability/performance of the Elasticsearch cluster depending on the number of nodes. I have a physical server (with 8 cores, 30 GB memory) and on that physical server I create\* 4 virtual machines\*, each assigned with 2 cores and 4GB of memory. On each virtual machine I install Elasticsearch, therefore each machine represents a separate node in my Elasticsearch cluster. The data contains\* about 7 million documents\*, I have\* 5 shards and replication\_count=1 (default configuration)\*. I am executing a set of tests on the cluster with different cluster-configurations. At first I assign only 1 node to the cluster and execute the tests, then I assign 2 nodes to the cluster and execute the same tests again, then 3 nodes etc. The tests do not contain any fancy features (no facets, highlighting, etc), but only filters and queries. I expected that for each additional node in the cluster I would get a linear improvement of the query response time. Because each node contains a bit of the data (shard) and so the query could be executed on each shard at the same time. But it turns out that the response time of the query is not improving nor is it getting worse, _it almost stays the same_.... So my question: Are these results expected, that _the query response time does NOT improve when adding an additional node?_ I execute the test queries one after another and not in parallel. Is Elasticsearch made just to handle a high load of requests, but not for improving the query time of a single request when I add additional nodes to the cluster? I mean, would I see only an improvement for each additional node, when I would run the tests in _parallel_, because then the query load is distributed? Regards, Herbert -- 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 [elasticsearch+unsubscribe@googlegroups.com](mailto:elasticsearch+unsubscribe@googlegroups.com). To view this discussion on the web visit [https://groups.google.com/d/msgid/elasticsearch/5d210ab6-08c0-4512-a6ee-fff677ae7207%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/5d210ab6-08c0-4512-a6ee-fff677ae7207%40googlegroups.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![jprante](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/jprante/32/44941_2.png) [@jprante](https://discuss.elastic.co/u/jprante)\ **Post date:** [March 24, 2014, 2:33pm UTC](https://discuss.elastic.co/t/query-response-time-does-not-improve-by-adding-additional-nodes/16557/2 "2014-03-24T14:33:31Z")
For better results - you should align the number of nodes n with the shard count c, so that c/n = i where i is an integer - 7 million docs may be too few to see any effect, this depends on the node capacity - for higher perfomance, you should use one JVM per machine, not 4 virtual machines on one machine The query response time will not get faster by adding nodes. The query response time on a single shard is limited by hardware factors (like CPU power, RAM, disk speed) and some software settings (ES settings, ES caches). The query response time will scale over nodes, that is, if you have saturated one node, you can add more nodes, start over to add more docs, while the query response time will not get higher by the number of added docs. The reason is, ES submits the queries to the shards on the nodes in parallel, so it makes no difference if there is one or thousands nodes in the cluster. Of course you should run query tests in parallel, if you want to measure the cluster capacity / throughput. Jörg On Mon, Mar 24, 2014 at 9:54 AM, Herbert Bodner [herbert.bodner@gmail.com](mailto:herbert.bodner@gmail.com)wrote: > Are these results expected, that _the query response time does NOT > improve when adding an additional node?_ -- 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 [elasticsearch+unsubscribe@googlegroups.com](mailto:elasticsearch+unsubscribe@googlegroups.com). To view this discussion on the web visit [https://groups.google.com/d/msgid/elasticsearch/CAKdsXoGaMyKWYGkPnn8wo\_kzm4W%2BoSv62bNQNU0G2Dws9pK1hg%40mail.gmail.com](https://groups.google.com/d/msgid/elasticsearch/CAKdsXoGaMyKWYGkPnn8wo_kzm4W%2BoSv62bNQNU0G2Dws9pK1hg%40mail.gmail.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![Herbert\_Bodner](https://avatars.discourse-cdn.com/v4/letter/h/a4c791/32.png) [@Herbert\_Bodner](https://discuss.elastic.co/u/Herbert_Bodner)\ **Post date:** [March 26, 2014, 5:08pm UTC](https://discuss.elastic.co/t/query-response-time-does-not-improve-by-adding-additional-nodes/16557/3 "2014-03-26T17:08:11Z")
thanks Jörg for your response. I guess the bottleneck is the I/O (as you suggested). So it does not matter if I add additional memory or CPU power to the Elasticsearch cluster (with adding additional virtual machines), because all nodes run on the same physical server with limited I/O capacity. If one node already uses the whole I/O capacity, then adding additional nodes (on the same physical server) does not help. cheers -- 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 [elasticsearch+unsubscribe@googlegroups.com](mailto:elasticsearch+unsubscribe@googlegroups.com). To view this discussion on the web visit [https://groups.google.com/d/msgid/elasticsearch/c717f35d-8ecc-4f57-a175-225b166c9aed%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/c717f35d-8ecc-4f57-a175-225b166c9aed%40googlegroups.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\ **Post date:** [July 6, 2017, 1:40am UTC](https://discuss.elastic.co/t/query-response-time-does-not-improve-by-adding-additional-nodes/16557/4 "2017-07-06T01:40:29Z")