# How does the memory usage for terms facets work? **URL:** \ **Category:** Elasticsearch\ **Created:** [April 24, 2013, 6:20pm UTC](https://discuss.elastic.co/t/how-does-the-memory-usage-for-terms-facets-work/11684 "2013-04-24T18:20:13Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![jieren](https://avatars.discourse-cdn.com/v4/letter/j/e9a140/32.png) [@jieren](https://discuss.elastic.co/u/jieren)\ **Post date:** [April 24, 2013, 6:20pm UTC](https://discuss.elastic.co/t/how-does-the-memory-usage-for-terms-facets-work/11684/1 "2013-04-24T18:20:13Z")
Hi everyone I am still a bit unclear on how terms facets load values into memory. What people have said is that it loads all the values into memory. Does that means it loads all the unique values of the fields into memory or the values of the fields per document? For example Suppose I have documents: { "id" : "1", "tags" : ["foo", "bar"] } { "id" : "2", "tags" : ["foo", "bar"] } Will "foo" and "bar" be loaded once or twice into memory? Thank you! Jieren -- 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). For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). ---
**Author:** ![dadoonet](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/dadoonet/32/137187_2.png) [@dadoonet](https://discuss.elastic.co/u/dadoonet)\ **Post date:** [April 24, 2013, 6:32pm UTC](https://discuss.elastic.co/t/how-does-the-memory-usage-for-terms-facets-work/11684/2 "2013-04-24T18:32:38Z")
Unique ones. So facetting on few unique values will scale really easily. But if you facet on a comment field for example, it will load (too) many terms in memory. HTH -- David 😉 Twitter : @dadoonet / @elasticsearchfr / @scrutmydocs Le 24 avr. 2013 à 20:20, jieren [jieren@klout.com](mailto:jieren@klout.com) a écrit : > Hi everyone > > I am still a bit unclear on how terms facets load values into memory. > > What people have said is that it loads all the values into memory. Does that means it loads all the unique values of the fields into memory or the values of the fields per document? > > For example > > Suppose I have documents: > { > "id" : "1", > "tags" : ["foo", "bar"] > } > > { > "id" : "2", > "tags" : ["foo", "bar"] > } > > Will "foo" and "bar" be loaded once or twice into memory? > > Thank you! > Jieren > > -- > 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). > For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). -- 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). For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). ---
**Author:** ![jieren](https://avatars.discourse-cdn.com/v4/letter/j/e9a140/32.png) [@jieren](https://discuss.elastic.co/u/jieren)\ **Post date:** [April 24, 2013, 8:52pm UTC](https://discuss.elastic.co/t/how-does-the-memory-usage-for-terms-facets-work/11684/3 "2013-04-24T20:52:32Z")
Thanks for the fast answer! On Wednesday, April 24, 2013 11:32:38 AM UTC-7, David Pilato wrote: > Unique ones. > > So facetting on few unique values will scale really easily. > But if you facet on a comment field for example, it will load (too) many > terms in memory. > > HTH > > -- > David 😉 > Twitter : @dadoonet / @elasticsearchfr / @scrutmydocs > > Le 24 avr. 2013 à 20:20, jieren \<[jie...@klout.com](mailto:jie...@klout.com) \\> a écrit : > > Hi everyone > > I am still a bit unclear on how terms facets load values into memory. > > What people have said is that it loads all the values into memory. Does > that means it loads all the unique values of the fields into memory or the > values of the fields per document? > > For example > > Suppose I have documents: > { > "id" : "1", > "tags" : ["foo", "bar"] > } > > { > "id" : "2", > "tags" : ["foo", "bar"] > } > > Will "foo" and "bar" be loaded once or twice into memory? > > Thank you! > Jieren > > -- > 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 [elasticsearc...@googlegroups.com](mailto:elasticsearc...@googlegroups.com) \. > For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). -- 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). For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). ---
**Author:** ![Marcin\_Dojwa](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/marcin_dojwa/32/2307_2.png) [@Marcin\_Dojwa](https://discuss.elastic.co/u/Marcin_Dojwa)\ **Post date:** [April 25, 2013, 1:23pm UTC](https://discuss.elastic.co/t/how-does-the-memory-usage-for-terms-facets-work/11684/4 "2013-04-25T13:23:45Z")
This is not clarified anywhere. This description of memory usage by field cache should help everyone. 1. Estimations (in Bytes) for a single Lucene segment, field cache for the following types: =\> numbers (including datetime formats) 48 (JAVA structures for docs list) + 4 \* max\_doc\_id \* max\_array\_size - 8 (JAVA structures for unique term list) + unique\_terms\_count \* 4 =\> strings 48 (JAVA structures for docs list) + 4 \* max\_doc\_id \* max\_array\_size + 8 (JAVA structures for unique term list) + unique\_terms\_count \* (4 + string\_size\_in\_bytes) max\_doc\_id - the highest lucene id + 1 (in coresponding segment) string\_size\_in\_bytes(max) = 4 \* string\_len (UTF8) max\_array\_size - maximum number of elements (through all the documents in segment) in multivalued field. 1. Since the field cache is per segment, unique terms array is kept per segment too Check that you use multivalued vield as tags. So even if you have only 1 document with eg. 10 elements in tags and the rest of the documents have 1 element in tags (I still mean in a single Lucene segment), the field cache still uses bidirectional array for document list with Y-size = 10, so it takes the same amount of memory as if all the documents have 10 values in tags. So one thins is unique terms - this can be estimated very simple. But the second thing is an array with document pointers - this can be very heavy. I strongly do NOT recommend using facets on multivalued fields, in this case use nested array - then each element of the field is a separated document and here the situation does not occur. In my case optimizing multivalued fields and switching to nested gave me about 2GB of field cache usage instead of 17GB 🙂 Remember that this cache can be estimated in a single segment. Each shard consists of 10-20 segments (for default ES settings). Each segment max size (by default) is 5GB and merge policy takes care to keep a few big segments (up to 5GB), most segments are small (it depends of shard size of course). You can check segments sizes getting localhost:9200//\_segments. I hope that this will solve your problems with field cache exploding 🙂 It solved mine 🙂 Best regards. Marcin Dojwa 2013/4/24 jieren [jieren@klout.com](mailto:jieren@klout.com) > Thanks for the fast answer! > > On Wednesday, April 24, 2013 11:32:38 AM UTC-7, David Pilato wrote: > > > Unique ones. > > > > So facetting on few unique values will scale really easily. > > But if you facet on a comment field for example, it will load (too) many > > terms in memory. > > > > HTH > > > > -- > > David 😉 > > Twitter : @dadoonet / @elasticsearchfr / @scrutmydocs > > > > Le 24 avr. 2013 à 20:20, jieren [jie...@klout.com](mailto:jie...@klout.com) a écrit : > > > > Hi everyone > > > > I am still a bit unclear on how terms facets load values into memory. > > > > What people have said is that it loads all the values into memory. Does > > that means it loads all the unique values of the fields into memory or the > > values of the fields per document? > > > > For example > > > > Suppose I have documents: > > { > > "id" : "1", > > "tags" : ["foo", "bar"] > > } > > > > { > > "id" : "2", > > "tags" : ["foo", "bar"] > > } > > > > Will "foo" and "bar" be loaded once or twice into memory? > > > > Thank you! > > Jieren > > > > -- > > 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 elasticsearc...@\*\*[googlegroups.com](http://googlegroups.com). > > > > For more options, visit [https://groups.google.com/\*\*groups/opt\_out](https://groups.google.com/**groups/opt_out)[https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out) > > . > > > > -- > > 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). > > For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). -- 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). For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). ---
**Author:** ![Yuan\_Xu](https://avatars.discourse-cdn.com/v4/letter/y/7ba0ec/32.png) [@Yuan\_Xu](https://discuss.elastic.co/u/Yuan_Xu)\ **Post date:** [April 27, 2013, 2:31am UTC](https://discuss.elastic.co/t/how-does-the-memory-usage-for-terms-facets-work/11684/5 "2013-04-27T02:31:26Z")
Hi, Thanks a lot for your detailed explaination... I got two questions: 1. Those calculating term facet formulas based on which ES version? 2. multivalued term means what? a field contains multivalues or the multi field type offered by ES mapping? Thanks in advance On Thursday, April 25, 2013 2:20:13 AM UTC+8, jieren wrote: > Hi everyone > > I am still a bit unclear on how terms facets load values into memory. > > What people have said is that it loads all the values into memory. Does > that means it loads all the unique values of the fields into memory or the > values of the fields per document? > > For example > > Suppose I have documents: > { > "id" : "1", > "tags" : ["foo", "bar"] > } > > { > "id" : "2", > "tags" : ["foo", "bar"] > } > > Will "foo" and "bar" be loaded once or twice into memory? > > Thank you! > Jieren -- 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). For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). ---
**Author:** ![Ivan](https://avatars.discourse-cdn.com/v4/letter/i/df788c/32.png) [@Ivan](https://discuss.elastic.co/u/Ivan)\ **Post date:** [April 28, 2013, 2:31am UTC](https://discuss.elastic.co/t/how-does-the-memory-usage-for-terms-facets-work/11684/6 "2013-04-28T02:31:48Z")
1. I believe Marcin is referring to the field cache structure found in versions pre-0.90. The latest version does improve on the use case with high-cardinality fields, but how and by how much I do not know (still on 0.20). 2. The former (field contains multivalues). Multi-field essentially creates two or more fields under the hood (which in turn can also be multi-valued), so the original field is not sharing the same Lucene field. -- Ivan On Fri, Apr 26, 2013 at 7:31 PM, Yuan Xu [lemon8292@gmail.com](mailto:lemon8292@gmail.com) wrote: > Hi, > > Thanks a lot for your detailed explaination... > > I got two questions: > > 1. Those calculating term facet formulas based on which ES version? > > 2. multivalued term means what? a field contains multivalues or the multi > field type offered by ES mapping? > > Thanks in advance > > On Thursday, April 25, 2013 2:20:13 AM UTC+8, jieren wrote: > > > Hi everyone > > > > I am still a bit unclear on how terms facets load values into memory. > > > > What people have said is that it loads all the values into memory. Does > > that means it loads all the unique values of the fields into memory or the > > values of the fields per document? > > > > For example > > > > Suppose I have documents: > > { > > "id" : "1", > > "tags" : ["foo", "bar"] > > } > > > > { > > "id" : "2", > > "tags" : ["foo", "bar"] > > } > > > > Will "foo" and "bar" be loaded once or twice into memory? > > > > Thank you! > > Jieren > > > > -- > > 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). > > For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). -- 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). For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). ---
**Author:** ![Marcin\_Dojwa](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/marcin_dojwa/32/2307_2.png) [@Marcin\_Dojwa](https://discuss.elastic.co/u/Marcin_Dojwa)\ **Post date:** [May 1, 2013, 11:29am UTC](https://discuss.elastic.co/t/how-does-the-memory-usage-for-terms-facets-work/11684/7 "2013-05-01T11:29:19Z")
Hi, 1. Yes, these calculations refer to 0.20.6 2. Like Ivan said, eg. arrays. Best regards. Marcin Dojwa 2013/4/28 Ivan Brusic [ivan@brusic.com](mailto:ivan@brusic.com) > 1. I believe Marcin is referring to the field cache structure found in > versions pre-0.90. The latest version does improve on the use case with > high-cardinality fields, but how and by how much I do not know (still on > 0.20). > > 2. The former (field contains multivalues). Multi-field essentially > creates two or more fields under the hood (which in turn can also be > multi-valued), so the original field is not sharing the same Lucene field. > > -- > Ivan > > On Fri, Apr 26, 2013 at 7:31 PM, Yuan Xu [lemon8292@gmail.com](mailto:lemon8292@gmail.com) wrote: > > > Hi, > > > > Thanks a lot for your detailed explaination... > > > > I got two questions: > > > > 1. Those calculating term facet formulas based on which ES version? > > > > 2. multivalued term means what? a field contains multivalues or the > > multi field type offered by ES mapping? > > > > Thanks in advance > > > > On Thursday, April 25, 2013 2:20:13 AM UTC+8, jieren wrote: > > > > > Hi everyone > > > > > > I am still a bit unclear on how terms facets load values into memory. > > > > > > What people have said is that it loads all the values into memory. Does > > > that means it loads all the unique values of the fields into memory or the > > > values of the fields per document? > > > > > > For example > > > > > > Suppose I have documents: > > > { > > > "id" : "1", > > > "tags" : ["foo", "bar"] > > > } > > > > > > { > > > "id" : "2", > > > "tags" : ["foo", "bar"] > > > } > > > > > > Will "foo" and "bar" be loaded once or twice into memory? > > > > > > Thank you! > > > Jieren > > > > > > -- > > > 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). > > > For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). > > -- > 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). > For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). -- 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). For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). ---
**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, 2:38am UTC](https://discuss.elastic.co/t/how-does-the-memory-usage-for-terms-facets-work/11684/8 "2017-07-06T02:38:51Z")