# Nested vs Parent-Child - index and search side differences **URL:** \ **Category:** Elasticsearch\ **Created:** [June 17, 2014, 6:49pm UTC](https://discuss.elastic.co/t/nested-vs-parent-child-index-and-search-side-differences/18166 "2014-06-17T18:49:14Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Srinivasan\_Ramaswamy](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/srinivasan_ramaswamy/32/74106_2.png) [@Srinivasan\_Ramaswamy](https://discuss.elastic.co/u/Srinivasan_Ramaswamy)\ **Post date:** [June 17, 2014, 6:49pm UTC](https://discuss.elastic.co/t/nested-vs-parent-child-index-and-search-side-differences/18166/1 "2014-06-17T18:49:14Z")
I searched the forum and internet in general, but i couldn't find clear answers about the differences in scoring. And most of the answers are pretty old. I would like to know all the important current differences/comparison between nested and parent-child documents. What i understood so far 1. parent and child are two different lucene docs (and guaranteed to be in same shard). nested docs are stored as a separate doc using some internal representation and they are also in the same shard as parent doc. 2. using nested document gives significantly better performance compared to parent-child documents. 3. any update to a nested document will trigger the whole parent document to be reindexed, but any update to child will reindex only the child doc 4. when you apply a filter on nested field, the filter will work but all the nested docs will be returned along with the parent (its a feature in progress [https://github.com/elasticsearch/elasticsearch/issues/3022](https://github.com/elasticsearch/elasticsearch/issues/3022) ). we do not have this problem with parent-child. Questions or need to confirm my understanding 1. using nested documents will let me sort the documents based on fields in the nested documents, on the other hand i cannot sort by fields in child docs. (feature in progress [https://github.com/elasticsearch/elasticsearch/issues/2917](https://github.com/elasticsearch/elasticsearch/issues/2917)) 2. filtering results based on a field is possible with both nested and parent-child documents I am curious to know other differences from ranking/scoring perspective. I would ideally like to score the parent documents by an aggregate function (sum or avg) of a nested/child field. Any thoughts anyone ? Thanks Srini -- 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/8183aa8d-1efc-40e5-8555-120bca8ff426%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/8183aa8d-1efc-40e5-8555-120bca8ff426%40googlegroups.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![jpountz](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/jpountz/32/45836_2.png) [@jpountz](https://discuss.elastic.co/u/jpountz)\ **Post date:** [June 17, 2014, 11:30pm UTC](https://discuss.elastic.co/t/nested-vs-parent-child-index-and-search-side-differences/18166/2 "2014-06-17T23:30:14Z")
Your understanding is correct. To add more to it, nested documents are stored in contiguous blocks in the index, making it very fast to resolve the parent given a child and vice-versa. On the other hand for parent/child there is sort or a hash table maintained on top of the index to match parents with children. This makes indexing more flexible but search much slower. About your questions: 1. Indeed you cannot sort by fields of a child doc. 2. Correct. My recommendation would be to only use parent/child when nested documents are not applicable. They are much faster and memory-efficient at search time. But sometimes, the need to reindex all nested documents might prove not practical in which case parent/child might be an alternative. On Tue, Jun 17, 2014 at 8:49 PM, Srinivasan Ramaswamy [ursvasan@gmail.com](mailto:ursvasan@gmail.com) wrote: > I searched the forum and internet in general, but i couldn't find clear > answers about the differences in scoring. And most of the answers are > pretty old. I would like to know all the important current > differences/comparison between nested and parent-child documents. > > What i understood so far > > 1. parent and child are two different lucene docs (and guaranteed to be in > same shard). nested docs are stored as a separate doc using some internal > representation and they are also in the same shard as parent doc. > 2. using nested document gives significantly better performance compared > to parent-child documents. > 3. any update to a nested document will trigger the whole parent document > to be reindexed, but any update to child will reindex only the child doc > 4. when you apply a filter on nested field, the filter will work but all > the nested docs will be returned along with the parent (its a feature in > progress [https://github.com/elasticsearch/elasticsearch/issues/3022](https://github.com/elasticsearch/elasticsearch/issues/3022) ). > we do not have this problem with parent-child. > > Questions or need to confirm my understanding > > 1. using nested documents will let me sort the documents based on fields > in the nested documents, on the other hand i cannot sort by fields in child > docs. (feature in progress > [https://github.com/elasticsearch/elasticsearch/issues/2917](https://github.com/elasticsearch/elasticsearch/issues/2917)) > 2. filtering results based on a field is possible with both nested and > parent-child documents > > I am curious to know other differences from ranking/scoring perspective. I > would ideally like to score the parent documents by an aggregate function > (sum or avg) of a nested/child field. Any thoughts anyone ? > > Thanks > Srini > > -- > 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/8183aa8d-1efc-40e5-8555-120bca8ff426%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/8183aa8d-1efc-40e5-8555-120bca8ff426%40googlegroups.com) > [https://groups.google.com/d/msgid/elasticsearch/8183aa8d-1efc-40e5-8555-120bca8ff426%40googlegroups.com?utm\_medium=email&utm\_source=footer](https://groups.google.com/d/msgid/elasticsearch/8183aa8d-1efc-40e5-8555-120bca8ff426%40googlegroups.com?utm_medium=email&utm_source=footer) > . > For more options, visit [https://groups.google.com/d/optout](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 [elasticsearch+unsubscribe@googlegroups.com](mailto:elasticsearch+unsubscribe@googlegroups.com). To view this discussion on the web visit [https://groups.google.com/d/msgid/elasticsearch/CAL6Z4j59Nz6UT29%2BnY\_zzUT34ApQOH4%3DLcnzA5nKSqQ\_SSnGgw%40mail.gmail.com](https://groups.google.com/d/msgid/elasticsearch/CAL6Z4j59Nz6UT29%2BnY_zzUT34ApQOH4%3DLcnzA5nKSqQ_SSnGgw%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, 1:21am UTC](https://discuss.elastic.co/t/nested-vs-parent-child-index-and-search-side-differences/18166/3 "2017-07-06T01:21:40Z")