# Data distribution over shards and replicas **URL:** \ **Category:** Elasticsearch\ **Created:** [March 31, 2014, 7:49pm UTC](https://discuss.elastic.co/t/data-distribution-over-shards-and-replicas/16725 "2014-03-31T19:49:52Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![bagui](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/bagui/32/960_2.png) [@bagui](https://discuss.elastic.co/u/bagui)\ **Post date:** [March 31, 2014, 7:49pm UTC](https://discuss.elastic.co/t/data-distribution-over-shards-and-replicas/16725/1 "2014-03-31T19:49:52Z")
Hi, I've started working on elasticsearch and having some doubts about shards and replicas and how they handle data. I don't have any prior knowledge on Lucene. As I know lucene will split data in segments and store in disk, and shard is the lucene index itself. Some of the doubts which I have is... 1. There are two way we can do shard allocation, one in cluster level with config settings and another in index level settings. Suppose in cluster level I mentioned max shard is 3 and in index level I mentioned 5 shards, how the shards will be allocated? I have one cluster one node. 2. Suppose, one index is having 5 shards and 2 replicas and I'm pushing data in bulk api, how the data will be stored? Is same data will be stored in 5 shards or the data will split and store in chunks in 5 shards? How replicas will have backup of data of all 5 shards? 3. Suppose I have 5 nodes and 10 shards are distributed over the nodes, 2 shards each. So when I index new documents how the data will be stored in over the nodes? Suppose the 5th node goes down suddenly which is holding 9th and 10th shard. Now do I loose all the data stored in 9th and 10th shard or the data are already copied in rest of the nodes ? Please explain. Thanks, Subhadip -- 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/4ac575bd-0d0a-4f5f-972e-7f3c54f2eb85%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/4ac575bd-0d0a-4f5f-972e-7f3c54f2eb85%40googlegroups.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![warkolm](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/warkolm/32/39224_2.png) [@warkolm](https://discuss.elastic.co/u/warkolm)\ **Post date:** [March 31, 2014, 8:01pm UTC](https://discuss.elastic.co/t/data-distribution-over-shards-and-replicas/16725/2 "2014-03-31T20:01:24Z")
1 - it will use 5 as you've specifically set that, anything you don't specify will just use the cluster default. 2 - The data isn't replicated into all the shards, it splits the complete data up into 5 shards. Then each replica set will contain a copy of the data, which is then also sharded. 3 - ES will distribute data across all shards as best it can. It will also not store the replicas for a shard on the same node as the primary. So if a node that holds a primary shard dies, thena secondary shard will be promoted to primary. Regards, Mark Walkom Infrastructure Engineer Campaign Monitor email: [markw@campaignmonitor.com](mailto:markw@campaignmonitor.com) web: [www.campaignmonitor.com](http://www.campaignmonitor.com) On 1 April 2014 06:49, Subhadip Bagui [i.bagui@gmail.com](mailto:i.bagui@gmail.com) wrote: > Hi, > > I've started working on elasticsearch and having some doubts about shards > and replicas and how they handle data. I don't have any prior knowledge on > Lucene. > As I know lucene will split data in segments and store in disk, and shard > is the lucene index itself. Some of the doubts which I have is... > > 1. There are two way we can do shard allocation, one in cluster level with > config settings and another in index level settings. Suppose in cluster > level I mentioned max shard is 3 and in index level I mentioned 5 shards, > how the shards will be allocated? I have one cluster one node. > > 2. Suppose, one index is having 5 shards and 2 replicas and I'm pushing > data in bulk api, how the data will be stored? Is same data will be stored > in 5 shards or the data will split and store in chunks in 5 shards? How > replicas will have backup of data of all 5 shards? > > 3. Suppose I have 5 nodes and 10 shards are distributed over the nodes, 2 > shards each. So when I index new documents how the data will be stored in > over the nodes? > Suppose the 5th node goes down suddenly which is holding 9th and 10th > shard. Now do I loose all the data stored in 9th and 10th shard or the data > are already copied in rest of the nodes ? > > Please explain. > > Thanks, > Subhadip > > -- > 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/4ac575bd-0d0a-4f5f-972e-7f3c54f2eb85%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/4ac575bd-0d0a-4f5f-972e-7f3c54f2eb85%40googlegroups.com)[https://groups.google.com/d/msgid/elasticsearch/4ac575bd-0d0a-4f5f-972e-7f3c54f2eb85%40googlegroups.com?utm\_medium=email&utm\_source=footer](https://groups.google.com/d/msgid/elasticsearch/4ac575bd-0d0a-4f5f-972e-7f3c54f2eb85%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/CAEM624anWNJjEnTDQuUqaZ2Wy8mmagth3Occ71QQMR\_WO0obtQ%40mail.gmail.com](https://groups.google.com/d/msgid/elasticsearch/CAEM624anWNJjEnTDQuUqaZ2Wy8mmagth3Occ71QQMR_WO0obtQ%40mail.gmail.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![bagui](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/bagui/32/960_2.png) [@bagui](https://discuss.elastic.co/u/bagui)\ **Post date:** [April 2, 2014, 1:21pm UTC](https://discuss.elastic.co/t/data-distribution-over-shards-and-replicas/16725/3 "2014-04-02T13:21:02Z")
Thanks Mark for the prompt reply, I have some more doubts 1. Suppose one index is running with 3 shards and 1 replica and other index is running with the cluster settings i.e. 5 shards 2 replica then total 3+1 or 5+2 shards will be available in cluster? I have installed elasticsearch-head plugin but the replica shard is not showing there. For data distribution, replica shard also keeps other index documents or it will be used to keep backup copy of data only. 1. So documents under same index will be split due to sharding and distribute over the shards right ? Can we push all the documents for same index in a particular shard? I don't want to use custom routing as then I need one field value common for all the documents. How can we find out which shard is holding which documents? 2. If I make one index with 2 shards and no replica and the node in cluster holding this 2 shards dies, then will I lose the data, or the data will have a copy in cluster level replica? If I have only 1 replica and the node holds the replica dies then how the backup will happen? -- 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/4d7d0243-dcd1-4ac7-9fef-1d6e44599ea1%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/4d7d0243-dcd1-4ac7-9fef-1d6e44599ea1%40googlegroups.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![warkolm](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/warkolm/32/39224_2.png) [@warkolm](https://discuss.elastic.co/u/warkolm)\ **Post date:** [April 2, 2014, 9:37pm UTC](https://discuss.elastic.co/t/data-distribution-over-shards-and-replicas/16725/4 "2014-04-02T21:37:12Z")
1 - Data from both will be available, you've just told ES not to use the defaults for one index. A replica is not a backup, it's a 1:1 replica so it will contain the same data as the primary shard. 2 - Not sure, but I don't think so as lucene will try to split things. Routing is the recommended method for what you want. 3 - Yes, although you are unlikely to have them both on one node unless it is a single node cluster. What do mean by backup? If you're talking about replicas instead then the cluster will build a new replica if one dies. Regards, Mark Walkom Infrastructure Engineer Campaign Monitor email: [markw@campaignmonitor.com](mailto:markw@campaignmonitor.com) web: [www.campaignmonitor.com](http://www.campaignmonitor.com) On 3 April 2014 00:21, Subhadip Bagui [i.bagui@gmail.com](mailto:i.bagui@gmail.com) wrote: > Thanks Mark for the prompt reply, I have some more doubts > > 1. Suppose one index is running with 3 shards and 1 replica and other > index is running with the cluster settings i.e. 5 shards 2 replica then > total 3+1 or 5+2 shards will be available in cluster? I have installed > elasticsearch-head plugin but the replica shard is not showing there. > > For data distribution, replica shard also keeps other index documents or > it will be used to keep backup copy of data only. > > 1. So documents under same index will be split due to sharding and > distribute over the shards right ? Can we push all the documents for same > index in a particular shard? I don't want to use custom routing as then I > need one field value common for all the documents. How can we find out > which shard is holding which documents? > > 2. If I make one index with 2 shards and no replica and the node in > cluster holding this 2 shards dies, then will I lose the data, or the data > will have a copy in cluster level replica? If I have only 1 replica and > the node holds the replica dies then how the backup will happen? > > -- > 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/4d7d0243-dcd1-4ac7-9fef-1d6e44599ea1%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/4d7d0243-dcd1-4ac7-9fef-1d6e44599ea1%40googlegroups.com)[https://groups.google.com/d/msgid/elasticsearch/4d7d0243-dcd1-4ac7-9fef-1d6e44599ea1%40googlegroups.com?utm\_medium=email&utm\_source=footer](https://groups.google.com/d/msgid/elasticsearch/4d7d0243-dcd1-4ac7-9fef-1d6e44599ea1%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/CAEM624YnT8-1mHTJ-%3D8RmZhmn5MZugJ0cL39zdKwifG8o98myw%40mail.gmail.com](https://groups.google.com/d/msgid/elasticsearch/CAEM624YnT8-1mHTJ-%3D8RmZhmn5MZugJ0cL39zdKwifG8o98myw%40mail.gmail.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![bagui](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/bagui/32/960_2.png) [@bagui](https://discuss.elastic.co/u/bagui)\ **Post date:** [April 3, 2014, 4:08am UTC](https://discuss.elastic.co/t/data-distribution-over-shards-and-replicas/16725/5 "2014-04-03T04:08:28Z")
Thanks a lot Mark. That explains a lot. By backup I meant copy of same data. One last question, for fast searching what will be the better selection? single index multiple shards or multiple index single shard? Can you please give some reference how lucene splits documents and store in shards. That will help to get better idea. Thanks, Subhadip -- 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/3785b01c-328f-4f4c-8dab-db93b73b2b5c%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/3785b01c-328f-4f4c-8dab-db93b73b2b5c%40googlegroups.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![warkolm](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/warkolm/32/39224_2.png) [@warkolm](https://discuss.elastic.co/u/warkolm)\ **Post date:** [April 3, 2014, 9:46am UTC](https://discuss.elastic.co/t/data-distribution-over-shards-and-replicas/16725/6 "2014-04-03T09:46:09Z")
Depends on your data and cluster configuration, but you probably don't want a single shard unless it's a tiny, tiny index. Regards, Mark Walkom Infrastructure Engineer Campaign Monitor email: [markw@campaignmonitor.com](mailto:markw@campaignmonitor.com) web: [www.campaignmonitor.com](http://www.campaignmonitor.com) On 3 April 2014 15:08, Subhadip Bagui [i.bagui@gmail.com](mailto:i.bagui@gmail.com) wrote: > Thanks a lot Mark. That explains a lot. > > By backup I meant copy of same data. > > One last question, for fast searching what will be the better selection? > single index multiple shards or multiple index single shard? > > Can you please give some reference how lucene splits documents and store > in shards. That will help to get better idea. > > Thanks, > Subhadip > > -- > 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/3785b01c-328f-4f4c-8dab-db93b73b2b5c%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/3785b01c-328f-4f4c-8dab-db93b73b2b5c%40googlegroups.com)[https://groups.google.com/d/msgid/elasticsearch/3785b01c-328f-4f4c-8dab-db93b73b2b5c%40googlegroups.com?utm\_medium=email&utm\_source=footer](https://groups.google.com/d/msgid/elasticsearch/3785b01c-328f-4f4c-8dab-db93b73b2b5c%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/CAEM624YK3iUQ7Gm4-nGtqyorz8F4U3GbJPwwAuOvft\_WBrLktQ%40mail.gmail.com](https://groups.google.com/d/msgid/elasticsearch/CAEM624YK3iUQ7Gm4-nGtqyorz8F4U3GbJPwwAuOvft_WBrLktQ%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, 1:38am UTC](https://discuss.elastic.co/t/data-distribution-over-shards-and-replicas/16725/7 "2017-07-06T01:38:35Z")