# Shards/routing documents imbalance problem **URL:** \ **Category:** Elasticsearch\ **Created:** [March 26, 2014, 10:30am UTC](https://discuss.elastic.co/t/shards-routing-documents-imbalance-problem/16604 "2014-03-26T10:30:36Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Han\_JU](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/han_ju/32/962_2.png) [@Han\_JU](https://discuss.elastic.co/u/Han_JU)\ **Post date:** [March 26, 2014, 10:30am UTC](https://discuss.elastic.co/t/shards-routing-documents-imbalance-problem/16604/1 "2014-03-26T10:30:36Z")
Hi, We've indexed 25M documents into a single index of 128 shards with 1 replica. The `routing` parameter is set to a path in the document, which is an int value: \_routing: { path: "some\_id" required: true } In out 25M documents, there's 167 distinct values of this "some\_id" and in our expectation, ElasticSearch will route these documents evenly across all shards. But we've found out that, out of 128 shards, there are 53 empty shards (with 0 document inside), or, 40% of the shards are not used at all. My question: - is this normal? Do we miss something in configuring routing? - does this imbalanced shard utilization affect indexing speed? We can confirm that all documents are correctly indexed and routing works (when searching with routing only 1 shard responds with the correct answer). ElasticSearch version is v1.0.1. Thanks! -- 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/f7e86ae2-14a8-4381-842d-53adf59ec43d%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/f7e86ae2-14a8-4381-842d-53adf59ec43d%40googlegroups.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![Kevin\_Wang](https://avatars.discourse-cdn.com/v4/letter/k/f6c823/32.png) [@Kevin\_Wang](https://discuss.elastic.co/u/Kevin_Wang)\ **Post date:** [March 26, 2014, 10:39am UTC](https://discuss.elastic.co/t/shards-routing-documents-imbalance-problem/16604/2 "2014-03-26T10:39:15Z")
ES will get the shard id by hash(routing)%num of shards, in your case, there are only 167 distinct values but have 128 shards, I think it's highly possible there is less than 128 distinct hash values. So some of the shard will not have any data. Kevin On Wednesday, March 26, 2014 9:30:36 PM UTC+11, Han JU wrote: > Hi, > > We've indexed 25M documents into a single index of 128 shards with 1 > replica. > The `routing` parameter is set to a path in the document, which is an int > value: > > \_routing: { > path: "some\_id" > required: true > } > > In out 25M documents, there's 167 distinct values of this "some\_id" and in > our expectation, Elasticsearch will route these documents evenly across all > shards. > But we've found out that, out of 128 shards, there are 53 empty shards > (with 0 document inside), or, 40% of the shards are not used at all. > > My question: > > - is this normal? Do we miss something in configuring routing? > - does this imbalanced shard utilization affect indexing speed? > > We can confirm that all documents are correctly indexed and routing works > (when searching with routing only 1 shard responds with the correct answer). > Elasticsearch version is v1.0.1. > > Thanks! -- 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/d8961b19-e024-4a04-83fa-48f4cd44b7c4%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/d8961b19-e024-4a04-83fa-48f4cd44b7c4%40googlegroups.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![Han\_JU](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/han_ju/32/962_2.png) [@Han\_JU](https://discuss.elastic.co/u/Han_JU)\ **Post date:** [March 26, 2014, 10:49am UTC](https://discuss.elastic.co/t/shards-routing-documents-imbalance-problem/16604/3 "2014-03-26T10:49:10Z")
Thanks for your reply. As far as I know, in Java, basic hash value of positive int/long value is just themselves (our ids are small values like 1125, 345 etc). So I calculated some\_id % 128, and I got 116 distinct values. But in reality there's a lot less shards in use. Does Elasticsearch use some special hash function? 在 2014年3月26日星期三UTC+1上午11时39分15秒，Kevin Wang写道： > ES will get the shard id by hash(routing)%num of shards, in your case, > there are only 167 distinct values but have 128 shards, I think it's highly > possible there is less than 128 distinct hash values. So some of the shard > will not have any data. > > Kevin > > On Wednesday, March 26, 2014 9:30:36 PM UTC+11, Han JU wrote: > > > Hi, > > > > We've indexed 25M documents into a single index of 128 shards with 1 > > replica. > > The `routing` parameter is set to a path in the document, which is an int > > value: > > > > \_routing: { > > path: "some\_id" > > required: true > > } > > > > In out 25M documents, there's 167 distinct values of this "some\_id" and > > in our expectation, Elasticsearch will route these documents evenly across > > all shards. > > But we've found out that, out of 128 shards, there are 53 empty shards > > (with 0 document inside), or, 40% of the shards are not used at all. > > > > My question: > > > > - is this normal? Do we miss something in configuring routing? > > - does this imbalanced shard utilization affect indexing speed? > > > > We can confirm that all documents are correctly indexed and routing works > > (when searching with routing only 1 shard responds with the correct answer). > > Elasticsearch version is v1.0.1. > > > > Thanks! -- 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/f54da2a0-0b7a-49fb-b852-b2200c862b4d%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/f54da2a0-0b7a-49fb-b852-b2200c862b4d%40googlegroups.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![Kevin\_Wang](https://avatars.discourse-cdn.com/v4/letter/k/f6c823/32.png) [@Kevin\_Wang](https://discuss.elastic.co/u/Kevin_Wang)\ **Post date:** [March 26, 2014, 10:58am UTC](https://discuss.elastic.co/t/shards-routing-documents-imbalance-problem/16604/4 "2014-03-26T10:58:36Z")
There are two hash functions implementation org.elasticsearch.cluster.routing.operation.hash.djb.DjbHashFunction and org.elasticsearch.cluster.routing.operation.hash.simple.SimpleHashFunction, default is DjbHashFunction. You can try get the hash by using DjbHashFunction.DJB\_HASH(you id) On Wednesday, March 26, 2014 9:49:10 PM UTC+11, Han JU wrote: > Thanks for your reply. > > As far as I know, in Java, basic hash value of positive int/long value is > just themselves (our ids are small values like 1125, 345 etc). > So I calculated some\_id % 128, and I got 116 distinct values. But in > reality there's a lot less shards in use. > > Does Elasticsearch use some special hash function? > > 在 2014年3月26日星期三UTC+1上午11时39分15秒，Kevin Wang写道： > > > ES will get the shard id by hash(routing)%num of shards, in your case, > > there are only 167 distinct values but have 128 shards, I think it's highly > > possible there is less than 128 distinct hash values. So some of the shard > > will not have any data. > > > > Kevin > > > > On Wednesday, March 26, 2014 9:30:36 PM UTC+11, Han JU wrote: > > > > > Hi, > > > > > > We've indexed 25M documents into a single index of 128 shards with 1 > > > replica. > > > The `routing` parameter is set to a path in the document, which is an > > > int value: > > > > > > \_routing: { > > > path: "some\_id" > > > required: true > > > } > > > > > > In out 25M documents, there's 167 distinct values of this "some\_id" and > > > in our expectation, Elasticsearch will route these documents evenly across > > > all shards. > > > But we've found out that, out of 128 shards, there are 53 empty shards > > > (with 0 document inside), or, 40% of the shards are not used at all. > > > > > > My question: > > > > > > - is this normal? Do we miss something in configuring routing? > > > - does this imbalanced shard utilization affect indexing speed? > > > > > > We can confirm that all documents are correctly indexed and routing > > > works (when searching with routing only 1 shard responds with the correct > > > answer). > > > Elasticsearch version is v1.0.1. > > > > > > Thanks! -- 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/9c8a9eba-2f0f-452f-98ac-34463da7f496%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/9c8a9eba-2f0f-452f-98ac-34463da7f496%40googlegroups.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![Han\_JU](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/han_ju/32/962_2.png) [@Han\_JU](https://discuss.elastic.co/u/Han_JU)\ **Post date:** [March 26, 2014, 11:51am UTC](https://discuss.elastic.co/t/shards-routing-documents-imbalance-problem/16604/5 "2014-03-26T11:51:24Z")
Thanks a lot Kevin. That DJB\_HASH result makes it clear for us. I think we'll just use the id value as hash. Do you guys know how to plugin a custom hash function? 在 2014年3月26日星期三UTC+1上午11时58分36秒，Kevin Wang写道： > There are two hash functions > implementation org.elasticsearch.cluster.routing.operation.hash.djb.DjbHashFunction > and org.elasticsearch.cluster.routing.operation.hash.simple.SimpleHashFunction, > default is DjbHashFunction. You can try get the hash by > using DjbHashFunction.DJB\_HASH(you id) > > On Wednesday, March 26, 2014 9:49:10 PM UTC+11, Han JU wrote: > > > Thanks for your reply. > > > > As far as I know, in Java, basic hash value of positive int/long value is > > just themselves (our ids are small values like 1125, 345 etc). > > So I calculated some\_id % 128, and I got 116 distinct values. But in > > reality there's a lot less shards in use. > > > > Does Elasticsearch use some special hash function? > > > > 在 2014年3月26日星期三UTC+1上午11时39分15秒，Kevin Wang写道： > > > > > ES will get the shard id by hash(routing)%num of shards, in your case, > > > there are only 167 distinct values but have 128 shards, I think it's highly > > > possible there is less than 128 distinct hash values. So some of the shard > > > will not have any data. > > > > > > Kevin > > > > > > On Wednesday, March 26, 2014 9:30:36 PM UTC+11, Han JU wrote: > > > > > > > Hi, > > > > > > > > We've indexed 25M documents into a single index of 128 shards with 1 > > > > replica. > > > > The `routing` parameter is set to a path in the document, which is an > > > > int value: > > > > > > > > \_routing: { > > > > path: "some\_id" > > > > required: true > > > > } > > > > > > > > In out 25M documents, there's 167 distinct values of this "some\_id" and > > > > in our expectation, Elasticsearch will route these documents evenly across > > > > all shards. > > > > But we've found out that, out of 128 shards, there are 53 empty shards > > > > (with 0 document inside), or, 40% of the shards are not used at all. > > > > > > > > My question: > > > > > > > > - is this normal? Do we miss something in configuring routing? > > > > - does this imbalanced shard utilization affect indexing speed? > > > > > > > > We can confirm that all documents are correctly indexed and routing > > > > works (when searching with routing only 1 shard responds with the correct > > > > answer). > > > > Elasticsearch version is v1.0.1. > > > > > > > > Thanks! -- 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/29da8ba5-ccab-40b0-9174-b6522408dd51%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/29da8ba5-ccab-40b0-9174-b6522408dd51%40googlegroups.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![Han\_JU](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/han_ju/32/962_2.png) [@Han\_JU](https://discuss.elastic.co/u/Han_JU)\ **Post date:** [March 27, 2014, 10:11am UTC](https://discuss.elastic.co/t/shards-routing-documents-imbalance-problem/16604/6 "2014-03-27T10:11:39Z")
Do you guys know how to plug in a custom hash function for routing parameter? 在 2014年3月26日星期三UTC+1下午12时51分24秒，Han JU写道： > Thanks a lot Kevin. > > That DJB\_HASH result makes it clear for us. I think we'll just use the id > value as hash. > Do you guys know how to plugin a custom hash function? > > 在 2014年3月26日星期三UTC+1上午11时58分36秒，Kevin Wang写道： > > > There are two hash functions > > implementation org.elasticsearch.cluster.routing.operation.hash.djb.DjbHashFunction > > and org.elasticsearch.cluster.routing.operation.hash.simple.SimpleHashFunction, > > default is DjbHashFunction. You can try get the hash by > > using DjbHashFunction.DJB\_HASH(you id) > > > > On Wednesday, March 26, 2014 9:49:10 PM UTC+11, Han JU wrote: > > > > > Thanks for your reply. > > > > > > As far as I know, in Java, basic hash value of positive int/long value > > > is just themselves (our ids are small values like 1125, 345 etc). > > > So I calculated some\_id % 128, and I got 116 distinct values. But in > > > reality there's a lot less shards in use. > > > > > > Does Elasticsearch use some special hash function? > > > > > > 在 2014年3月26日星期三UTC+1上午11时39分15秒，Kevin Wang写道： > > > > > > > ES will get the shard id by hash(routing)%num of shards, in your case, > > > > there are only 167 distinct values but have 128 shards, I think it's highly > > > > possible there is less than 128 distinct hash values. So some of the shard > > > > will not have any data. > > > > > > > > Kevin > > > > > > > > On Wednesday, March 26, 2014 9:30:36 PM UTC+11, Han JU wrote: > > > > > > > > > Hi, > > > > > > > > > > We've indexed 25M documents into a single index of 128 shards with 1 > > > > > replica. > > > > > The `routing` parameter is set to a path in the document, which is an > > > > > int value: > > > > > > > > > > \_routing: { > > > > > path: "some\_id" > > > > > required: true > > > > > } > > > > > > > > > > In out 25M documents, there's 167 distinct values of this "some\_id" > > > > > and in our expectation, Elasticsearch will route these documents evenly > > > > > across all shards. > > > > > But we've found out that, out of 128 shards, there are 53 empty shards > > > > > (with 0 document inside), or, 40% of the shards are not used at all. > > > > > > > > > > My question: > > > > > > > > > > - is this normal? Do we miss something in configuring routing? > > > > > - does this imbalanced shard utilization affect indexing speed? > > > > > > > > > > We can confirm that all documents are correctly indexed and routing > > > > > works (when searching with routing only 1 shard responds with the correct > > > > > answer). > > > > > Elasticsearch version is v1.0.1. > > > > > > > > > > Thanks! -- 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/24ea97ab-3795-4def-b284-33742e30a908%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/24ea97ab-3795-4def-b284-33742e30a908%40googlegroups.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![Kevin\_Wang](https://avatars.discourse-cdn.com/v4/letter/k/f6c823/32.png) [@Kevin\_Wang](https://discuss.elastic.co/u/Kevin_Wang)\ **Post date:** [March 27, 2014, 10:27am UTC](https://discuss.elastic.co/t/shards-routing-documents-imbalance-problem/16604/7 "2014-03-27T10:27:24Z")
You can add a class that implements HashFunction and set the setting "cluster.routing.operation.hash.type“ to that class. Regards, Kevin On Thursday, March 27, 2014 9:11:39 PM UTC+11, Han JU wrote: > Do you guys know how to plug in a custom hash function for routing > parameter? > > 在 2014年3月26日星期三UTC+1下午12时51分24秒，Han JU写道： > > > Thanks a lot Kevin. > > > > That DJB\_HASH result makes it clear for us. I think we'll just use the id > > value as hash. > > Do you guys know how to plugin a custom hash function? > > > > 在 2014年3月26日星期三UTC+1上午11时58分36秒，Kevin Wang写道： > > > > > There are two hash functions > > > implementation org.elasticsearch.cluster.routing.operation.hash.djb.DjbHashFunction > > > and org.elasticsearch.cluster.routing.operation.hash.simple.SimpleHashFunction, > > > default is DjbHashFunction. You can try get the hash by > > > using DjbHashFunction.DJB\_HASH(you id) > > > > > > On Wednesday, March 26, 2014 9:49:10 PM UTC+11, Han JU wrote: > > > > > > > Thanks for your reply. > > > > > > > > As far as I know, in Java, basic hash value of positive int/long value > > > > is just themselves (our ids are small values like 1125, 345 etc). > > > > So I calculated some\_id % 128, and I got 116 distinct values. But in > > > > reality there's a lot less shards in use. > > > > > > > > Does Elasticsearch use some special hash function? > > > > > > > > 在 2014年3月26日星期三UTC+1上午11时39分15秒，Kevin Wang写道： > > > > > > > > > ES will get the shard id by hash(routing)%num of shards, in your case, > > > > > there are only 167 distinct values but have 128 shards, I think it's highly > > > > > possible there is less than 128 distinct hash values. So some of the shard > > > > > will not have any data. > > > > > > > > > > Kevin > > > > > > > > > > On Wednesday, March 26, 2014 9:30:36 PM UTC+11, Han JU wrote: > > > > > > > > > > > Hi, > > > > > > > > > > > > We've indexed 25M documents into a single index of 128 shards with 1 > > > > > > replica. > > > > > > The `routing` parameter is set to a path in the document, which is an > > > > > > int value: > > > > > > > > > > > > \_routing: { > > > > > > path: "some\_id" > > > > > > required: true > > > > > > } > > > > > > > > > > > > In out 25M documents, there's 167 distinct values of this "some\_id" > > > > > > and in our expectation, Elasticsearch will route these documents evenly > > > > > > across all shards. > > > > > > But we've found out that, out of 128 shards, there are 53 empty > > > > > > shards (with 0 document inside), or, 40% of the shards are not used at all. > > > > > > > > > > > > My question: > > > > > > > > > > > > - is this normal? Do we miss something in configuring routing? > > > > > > - does this imbalanced shard utilization affect indexing speed? > > > > > > > > > > > > We can confirm that all documents are correctly indexed and routing > > > > > > works (when searching with routing only 1 shard responds with the correct > > > > > > answer). > > > > > > Elasticsearch version is v1.0.1. > > > > > > > > > > > > Thanks! -- 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/9817fbd7-5e75-4557-807f-276df5b3120d%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/9817fbd7-5e75-4557-807f-276df5b3120d%40googlegroups.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![Han\_JU](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/han_ju/32/962_2.png) [@Han\_JU](https://discuss.elastic.co/u/Han_JU)\ **Post date:** [March 27, 2014, 10:32am UTC](https://discuss.elastic.co/t/shards-routing-documents-imbalance-problem/16604/8 "2014-03-27T10:32:28Z")
Thanks but can you explain some detail? Say I have the class in `MyHashFunction.java`, how could I put it in ES? I need to modify the code of ES or ? 在 2014年3月27日星期四UTC+1上午11时27分24秒，Kevin Wang写道： > You can add a class that implements HashFunction and set the setting > "cluster.routing.operation.hash.type“ to that class. > > Regards, > Kevin > > On Thursday, March 27, 2014 9:11:39 PM UTC+11, Han JU wrote: > > > Do you guys know how to plug in a custom hash function for routing > > parameter? > > > > 在 2014年3月26日星期三UTC+1下午12时51分24秒，Han JU写道： > > > > > Thanks a lot Kevin. > > > > > > That DJB\_HASH result makes it clear for us. I think we'll just use the > > > id value as hash. > > > Do you guys know how to plugin a custom hash function? > > > > > > 在 2014年3月26日星期三UTC+1上午11时58分36秒，Kevin Wang写道： > > > > > > > There are two hash functions > > > > implementation org.elasticsearch.cluster.routing.operation.hash.djb.DjbHashFunction > > > > and org.elasticsearch.cluster.routing.operation.hash.simple.SimpleHashFunction, > > > > default is DjbHashFunction. You can try get the hash by > > > > using DjbHashFunction.DJB\_HASH(you id) > > > > > > > > On Wednesday, March 26, 2014 9:49:10 PM UTC+11, Han JU wrote: > > > > > > > > > Thanks for your reply. > > > > > > > > > > As far as I know, in Java, basic hash value of positive int/long value > > > > > is just themselves (our ids are small values like 1125, 345 etc). > > > > > So I calculated some\_id % 128, and I got 116 distinct values. But in > > > > > reality there's a lot less shards in use. > > > > > > > > > > Does Elasticsearch use some special hash function? > > > > > > > > > > 在 2014年3月26日星期三UTC+1上午11时39分15秒，Kevin Wang写道： > > > > > > > > > > > ES will get the shard id by hash(routing)%num of shards, in your > > > > > > case, there are only 167 distinct values but have 128 shards, I think it's > > > > > > highly possible there is less than 128 distinct hash values. So some of the > > > > > > shard will not have any data. > > > > > > > > > > > > Kevin > > > > > > > > > > > > On Wednesday, March 26, 2014 9:30:36 PM UTC+11, Han JU wrote: > > > > > > > > > > > > > Hi, > > > > > > > > > > > > > > We've indexed 25M documents into a single index of 128 shards with 1 > > > > > > > replica. > > > > > > > The `routing` parameter is set to a path in the document, which is > > > > > > > an int value: > > > > > > > > > > > > > > \_routing: { > > > > > > > path: "some\_id" > > > > > > > required: true > > > > > > > } > > > > > > > > > > > > > > In out 25M documents, there's 167 distinct values of this "some\_id" > > > > > > > and in our expectation, Elasticsearch will route these documents evenly > > > > > > > across all shards. > > > > > > > But we've found out that, out of 128 shards, there are 53 empty > > > > > > > shards (with 0 document inside), or, 40% of the shards are not used at all. > > > > > > > > > > > > > > My question: > > > > > > > > > > > > > > - is this normal? Do we miss something in configuring routing? > > > > > > > - does this imbalanced shard utilization affect indexing speed? > > > > > > > > > > > > > > We can confirm that all documents are correctly indexed and routing > > > > > > > works (when searching with routing only 1 shard responds with the correct > > > > > > > answer). > > > > > > > Elasticsearch version is v1.0.1. > > > > > > > > > > > > > > Thanks! -- 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/c8f96c79-76c1-42eb-8380-ecc044b44a7f%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/c8f96c79-76c1-42eb-8380-ecc044b44a7f%40googlegroups.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![Kevin\_Wang](https://avatars.discourse-cdn.com/v4/letter/k/f6c823/32.png) [@Kevin\_Wang](https://discuss.elastic.co/u/Kevin_Wang)\ **Post date:** [March 27, 2014, 10:37am UTC](https://discuss.elastic.co/t/shards-routing-documents-imbalance-problem/16604/9 "2014-03-27T10:37:58Z")
You can add that as a plugin, see [Elasticsearch Platform — Find real-time answers at scale | Elastic](http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/modules-plugins.html) On Thursday, March 27, 2014 9:32:28 PM UTC+11, Han JU wrote: > Thanks but can you explain some detail? > Say I have the class in `MyHashFunction.java`, how could I put it in ES? I > need to modify the code of ES or ? > > 在 2014年3月27日星期四UTC+1上午11时27分24秒，Kevin Wang写道： > > > You can add a class that implements HashFunction and set the setting > > "cluster.routing.operation.hash.type“ to that class. > > > > Regards, > > Kevin > > > > On Thursday, March 27, 2014 9:11:39 PM UTC+11, Han JU wrote: > > > > > Do you guys know how to plug in a custom hash function for routing > > > parameter? > > > > > > 在 2014年3月26日星期三UTC+1下午12时51分24秒，Han JU写道： > > > > > > > Thanks a lot Kevin. > > > > > > > > That DJB\_HASH result makes it clear for us. I think we'll just use the > > > > id value as hash. > > > > Do you guys know how to plugin a custom hash function? > > > > > > > > 在 2014年3月26日星期三UTC+1上午11时58分36秒，Kevin Wang写道： > > > > > > > > > There are two hash functions > > > > > implementation org.elasticsearch.cluster.routing.operation.hash.djb.DjbHashFunction > > > > > and org.elasticsearch.cluster.routing.operation.hash.simple.SimpleHashFunction, > > > > > default is DjbHashFunction. You can try get the hash by > > > > > using DjbHashFunction.DJB\_HASH(you id) > > > > > > > > > > On Wednesday, March 26, 2014 9:49:10 PM UTC+11, Han JU wrote: > > > > > > > > > > > Thanks for your reply. > > > > > > > > > > > > As far as I know, in Java, basic hash value of positive int/long > > > > > > value is just themselves (our ids are small values like 1125, 345 etc). > > > > > > So I calculated some\_id % 128, and I got 116 distinct values. But in > > > > > > reality there's a lot less shards in use. > > > > > > > > > > > > Does Elasticsearch use some special hash function? > > > > > > > > > > > > 在 2014年3月26日星期三UTC+1上午11时39分15秒，Kevin Wang写道： > > > > > > > > > > > > > ES will get the shard id by hash(routing)%num of shards, in your > > > > > > > case, there are only 167 distinct values but have 128 shards, I think it's > > > > > > > highly possible there is less than 128 distinct hash values. So some of the > > > > > > > shard will not have any data. > > > > > > > > > > > > > > Kevin > > > > > > > > > > > > > > On Wednesday, March 26, 2014 9:30:36 PM UTC+11, Han JU wrote: > > > > > > > > > > > > > > > Hi, > > > > > > > > > > > > > > > > We've indexed 25M documents into a single index of 128 shards with > > > > > > > > 1 replica. > > > > > > > > The `routing` parameter is set to a path in the document, which is > > > > > > > > an int value: > > > > > > > > > > > > > > > > \_routing: { > > > > > > > > path: "some\_id" > > > > > > > > required: true > > > > > > > > } > > > > > > > > > > > > > > > > In out 25M documents, there's 167 distinct values of this "some\_id" > > > > > > > > and in our expectation, Elasticsearch will route these documents evenly > > > > > > > > across all shards. > > > > > > > > But we've found out that, out of 128 shards, there are 53 empty > > > > > > > > shards (with 0 document inside), or, 40% of the shards are not used at all. > > > > > > > > > > > > > > > > My question: > > > > > > > > > > > > > > > > - is this normal? Do we miss something in configuring routing? > > > > > > > > - does this imbalanced shard utilization affect indexing speed? > > > > > > > > > > > > > > > > We can confirm that all documents are correctly indexed and routing > > > > > > > > works (when searching with routing only 1 shard responds with the correct > > > > > > > > answer). > > > > > > > > Elasticsearch version is v1.0.1. > > > > > > > > > > > > > > > > Thanks! -- 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/1ade0d24-ee99-4a00-8bf0-7a749271b58d%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/1ade0d24-ee99-4a00-8bf0-7a749271b58d%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/shards-routing-documents-imbalance-problem/16604/10 "2017-07-06T01:40:15Z")