# The relation of the amount of indexed documents, max\_expansions and prefix\_length in text\_phrase\_prefix **URL:** \ **Category:** Elasticsearch\ **Created:** [November 29, 2012, 12:02pm UTC](https://discuss.elastic.co/t/the-relation-of-the-amount-of-indexed-documents-max-expansions-and-prefix-length-in-text-phrase-prefix/9883 "2012-11-29T12:02:57Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![pcdinh](https://avatars.discourse-cdn.com/v4/letter/p/76d3ee/32.png) [@pcdinh](https://discuss.elastic.co/u/pcdinh)\ **Post date:** [November 29, 2012, 12:02pm UTC](https://discuss.elastic.co/t/the-relation-of-the-amount-of-indexed-documents-max-expansions-and-prefix-length-in-text-phrase-prefix/9883/1 "2012-11-29T12:02:57Z")
Hi all, I have an issue with ES 0.19.3 regarding to text\_phrase\_prefix query. When number of documents indexed in ES is small the following query works perfectly (type "New Y", not "New York" or "New Yo") curl -X DELETE [http://es1:9200/cities](http://es1:9200/cities) curl -X POST "[http://es1:9200/cities/city](http://es1:9200/cities/city)" -d '{ "city" : "New York" }' curl -X POST "[http://es1:9200/cities/city](http://es1:9200/cities/city)" -d '{ "city" : "North New York" }' curl -X POST "[http://es1:9200/cities/city](http://es1:9200/cities/city)" -d '{ "city" : "East New York" }' curl -XGET [http://es1:9200/cities/city/\_search?pretty=true](http://es1:9200/cities/city/_search?pretty=true) -d' { "fields":[ "city" ], "query":{ "text\_phrase\_prefix": { "city" : { "query": "New Y", "max\_expansions": 2, "prefix\_length": 2 } } }, "from":0, "size":20 }' returns all cities or areas has "New York" in their names. { "took" : 2, "timed\_out" : false, "\_shards" : { "total" : 5, "successful" : 5, "failed" : 0 }, "hits" : { "total" : 3, "max\_score" : 0.38356602, "hits" : [ { "\_index" : "cities", "\_type" : "city", "\_id" : "4ObkgggqS7uou1XLdwOkfA", "\_score" : 0.38356602, "fields" : { "city" : "New York" } }, { "\_index" : "cities", "\_type" : "city", "\_id" : "CZutMgvwSfa8O79Vajkshg", "\_score" : 0.30685282, "fields" : { "city" : "North New York" } }, { "\_index" : "cities", "\_type" : "city", "\_id" : "ZGA3gno9QnOIBg2MxxsPbg", "\_score" : 0.30685282, "fields" : { "city" : "East New York" } } ] } } However when the number of indexed document grows up (more than 30 000 cities or towns or areas in US), the above query does not work any more. I need to increase max\_expansions into a number that is greater than 17 (18 and greater to be specific) to make it work again. Any number that is smaller than 17 does not work. If I don't increase max\_expansions, I need to use keywords like: "New Yo" or "New York" curl -XGET [http://184.72.29.x:9200/cities/city/\_search?pretty=true](http://184.72.29.x:9200/cities/city/_search?pretty=true) -d' { "fields":[ "area\_label" ], "query":{ "text\_phrase\_prefix": { "area\_label" : { "query": "New Y", "max\_expansions": 18, "prefix\_length": 2 } } }, "from":0, "size":20 } ' returns { "took" : 7, "timed\_out" : false, "\_shards" : { "total" : 5, "successful" : 5, "failed" : 0 }, "hits" : { "total" : 3, "max\_score" : 111.86473, "hits" : [ { "\_index" : "cities", "\_type" : "city", "\_id" : "195232", "\_score" : 111.86473, "fields" : { "area\_label" : "New York" } }, { "\_index" : "cities", "\_type" : "city", "\_id" : "46727", "\_score" : 89.49178, "fields" : { "area\_label" : "North New York" } }, { "\_index" : "cities", "\_type" : "city", "\_id" : "46772", "\_score" : 89.49178, "fields" : { "area\_label" : "East New York" } } ] } } prefix\_length does not play any role in this case. I increase the value of prefix\_length to 20, the result is still the same. I don't understand why the number of 18 is magic in this case. I guess that there is a relationship between max\_expansions and the number of indexed document. So when the amount of indexed documents increases, I need to increase max\_expansions too or the above query does not work again. Am I missing something? Regards, Dinh -- ---
**Author:** ![Clinton\_Gormley](https://avatars.discourse-cdn.com/v4/letter/c/50afbb/32.png) [@Clinton\_Gormley](https://discuss.elastic.co/u/Clinton_Gormley)\ **Post date:** [November 29, 2012, 12:49pm UTC](https://discuss.elastic.co/t/the-relation-of-the-amount-of-indexed-documents-max-expansions-and-prefix-length-in-text-phrase-prefix/9883/2 "2012-11-29T12:49:36Z")
Hi Dinh > However when the number of indexed document grows up (more than 30 000 > cities or towns or areas in US), the above query does not work any > more. > I need to increase max\_expansions into a number that is greater than > 17 (18 and greater to be specific) to make it work again. Any number > that > is smaller than 17 does not work. If I don't increase max\_expansions, > I need to use keywords like: "New Yo" or "New York" > prefix\_length does not play any role in this case. I increase the > value of prefix\_length to 20, the result is still the same. prefix\_length is for fuzzy queries, not phrase\_prefix > I don't understand why the number of 18 is magic in this case. I guess > that there is a relationship between max\_expansions and the number of > indexed document. So when the amount of indexed documents increases, I > need to increase max\_expansions too or the above query does not work > again. To build a prefix query, it looks for all terms starting with your prefix 'y' and adds each term to your query, up to max\_expansions. The terms are sorted alphabetically. If you've indexed lots more data, than presumably you have a lot more terms between "ya" and "yo" than you had before. if you want to do partial matching of words, then a better idea is to use ngrams or edge-ngrams to index your data up front. it is more efficient at search time than using a prefix query. clint -- ---
**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, 3:02am UTC](https://discuss.elastic.co/t/the-relation-of-the-amount-of-indexed-documents-max-expansions-and-prefix-length-in-text-phrase-prefix/9883/3 "2017-07-06T03:02:13Z")