# How does "size" work under the hood? **URL:** \ **Category:** Elasticsearch\ **Created:** [July 11, 2014, 2:32pm UTC](https://discuss.elastic.co/t/how-does-size-work-under-the-hood/18603 "2014-07-11T14:32:20Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![x0ne\_2](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/x0ne_2/32/1405_2.png) [@x0ne\_2](https://discuss.elastic.co/u/x0ne_2)\ **Post date:** [July 11, 2014, 2:32pm UTC](https://discuss.elastic.co/t/how-does-size-work-under-the-hood/18603/1 "2014-07-11T14:32:20Z")
I am trying to figure out the best way to issue my queries as to not flood the heap with data I may not care about. Before each query, I do a count search type to identify how many results I am potentially dealing with. When I specify a "size" in my search query, how exactly does that impact results and the heap? If I run a query that matches 50k documents and I am only interested in 25 (specified by size), are all 50K still loaded into memory? Is there a way to get just the top 25 results off the query match without loading all hits into memory or is that how size actually works? -- 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/9837a8e5-ddf6-4684-8fe0-dd6909bcee48%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/9837a8e5-ddf6-4684-8fe0-dd6909bcee48%40googlegroups.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![nik9000](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/nik9000/32/44947_2.png) [@nik9000](https://discuss.elastic.co/u/nik9000)\ **Post date:** [July 11, 2014, 2:43pm UTC](https://discuss.elastic.co/t/how-does-size-work-under-the-hood/18603/2 "2014-07-11T14:43:09Z")
The first count query might not be needed because a normal query comes back with a count anyway. The size parameter ultimately translates into the size of a min heap. Worst case scenario space is just the size parameter times number of shards. Worst case scenario time is log(size) \* number of documents matched. If size is much smaller then number of documents matched then the average case tends to end up being more related to the number of documents matched then the size because most matches aren't better then whatever is collected in the heap. At some point the heap has to be sorted, sent back to the one node, merged, then fetched. The fetch may end up being slower then all of the rest of it. And may end up using more memory if you are loading source. Nik On Fri, Jul 11, 2014 at 10:32 AM, x0ne [brandon.s.dixon@gmail.com](mailto:brandon.s.dixon@gmail.com) wrote: > I am trying to figure out the best way to issue my queries as to not flood > the heap with data I may not care about. Before each query, I do a count > search type to identify how many results I am potentially dealing with. > When I specify a "size" in my search query, how exactly does that impact > results and the heap? If I run a query that matches 50k documents and I am > only interested in 25 (specified by size), are all 50K still loaded into > memory? Is there a way to get just the top 25 results off the query match > without loading all hits into memory or is that how size actually works? > > -- > 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/9837a8e5-ddf6-4684-8fe0-dd6909bcee48%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/9837a8e5-ddf6-4684-8fe0-dd6909bcee48%40googlegroups.com) > [https://groups.google.com/d/msgid/elasticsearch/9837a8e5-ddf6-4684-8fe0-dd6909bcee48%40googlegroups.com?utm\_medium=email&utm\_source=footer](https://groups.google.com/d/msgid/elasticsearch/9837a8e5-ddf6-4684-8fe0-dd6909bcee48%40googlegroups.com?utm_medium=email&utm_source=footer) > . > For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). -- 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/CAPmjWd3TJV-ZQ-wZMrfMR%2B9EQV\_V48onfCCmqr9P64T5eusSyA%40mail.gmail.com](https://groups.google.com/d/msgid/elasticsearch/CAPmjWd3TJV-ZQ-wZMrfMR%2B9EQV_V48onfCCmqr9P64T5eusSyA%40mail.gmail.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, 1:16am UTC](https://discuss.elastic.co/t/how-does-size-work-under-the-hood/18603/3 "2017-07-06T01:16:31Z")