# Number of replicas and query speed **URL:** \ **Category:** Elasticsearch\ **Created:** [January 9, 2012, 10:08am UTC](https://discuss.elastic.co/t/number-of-replicas-and-query-speed/6321 "2012-01-09T10:08:23Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![bogdanionescu](https://avatars.discourse-cdn.com/v4/letter/b/7cd45c/32.png) [@bogdanionescu](https://discuss.elastic.co/u/bogdanionescu)\ **Post date:** [January 9, 2012, 10:08am UTC](https://discuss.elastic.co/t/number-of-replicas-and-query-speed/6321/1 "2012-01-09T10:08:23Z")
Hello I have a 4 node cluster with 7.7M docs indexed. 5 shards. Fist I've tried with 1 replica (default config) and we tested the query speed. It worked fine. The we used the REST API to increase the number of replicas to 4 and after a while the nodes reflected this change (in shards dirs stored locally all had a copy of all the 5 shards). The problems is that the query speed was exactly the same as when using 1 replica config! Any ideas why this happens? Shouldn't be any improvement at all? ---
**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:** [January 9, 2012, 10:25am UTC](https://discuss.elastic.co/t/number-of-replicas-and-query-speed/6321/2 "2012-01-09T10:25:11Z")
Hiya > I have a 4 node cluster with 7.7M docs indexed. 5 shards. > Fist I've tried with 1 replica (default config) and we tested the > query speed. It worked fine. > The we used the REST API to increase the number of replicas to 4 and > after a while the nodes reflected this change (in shards dirs stored > locally all had a copy of all the 5 shards). > The problems is that the query speed was exactly the same as when > using 1 replica config! > Any ideas why this happens? Shouldn't be any improvement at all? ES still has to talk to exactly the same number of shards for your query. The fact that there are more of them to choose from doesn't affect your query speed. Where it will make a difference is when you reach the point that your 1 replica setup is too busy to cope with all of your queries. At that stage, having more replicas to choose from will help you to scale clint ---
**Author:** ![bogdanionescu](https://avatars.discourse-cdn.com/v4/letter/b/7cd45c/32.png) [@bogdanionescu](https://discuss.elastic.co/u/bogdanionescu)\ **Post date:** [January 9, 2012, 10:55am UTC](https://discuss.elastic.co/t/number-of-replicas-and-query-speed/6321/3 "2012-01-09T10:55:11Z")
I see... I agree the response time should be the same, but the I thought the throughput should increase. I'll try to increase the load and compare the results then. On Jan 9, 12:25 pm, Clinton Gormley [cl...@traveljury.com](mailto:cl...@traveljury.com) wrote: > Hiya > > > I have a 4 node cluster with 7.7M docs indexed. 5 shards. > > Fist I've tried with 1 replica (default config) and we tested the > > query speed. It worked fine. > > The we used the REST API to increase the number of replicas to 4 and > > after a while the nodes reflected this change (in shards dirs stored > > locally all had a copy of all the 5 shards). > > The problems is that the query speed was exactly the same as when > > using 1 replica config! > > Any ideas why this happens? Shouldn't be any improvement at all? > > ES still has to talk to exactly the same number of shards for your > query. The fact that there are more of them to choose from doesn't > affect your query speed. > > Where it will make a difference is when you reach the point that your 1 > replica setup is too busy to cope with all of your queries. At that > stage, having more replicas to choose from will help you to scale > > clint ---
**Author:** ![bogdanionescu](https://avatars.discourse-cdn.com/v4/letter/b/7cd45c/32.png) [@bogdanionescu](https://discuss.elastic.co/u/bogdanionescu)\ **Post date:** [January 9, 2012, 3:50pm UTC](https://discuss.elastic.co/t/number-of-replicas-and-query-speed/6321/4 "2012-01-09T15:50:03Z")
I did some tests under heavier load and I still could not see any improvement when using more replicas... On Jan 9, 12:55 pm, [bogdaniones...@yahoo.com](mailto:bogdaniones...@yahoo.com) wrote: > I see... I agree the response time should be the same, but the I > thought the throughput should increase. > I'll try to increase the load and compare the results then. > > On Jan 9, 12:25 pm, Clinton Gormley [cl...@traveljury.com](mailto:cl...@traveljury.com) wrote: > > > Hiya > > > > I have a 4 node cluster with 7.7M docs indexed. 5 shards. > > > Fist I've tried with 1 replica (default config) and we tested the > > > query speed. It worked fine. > > > The we used the REST API to increase the number of replicas to 4 and > > > after a while the nodes reflected this change (in shards dirs stored > > > locally all had a copy of all the 5 shards). > > > The problems is that the query speed was exactly the same as when > > > using 1 replica config! > > > Any ideas why this happens? Shouldn't be any improvement at all? > > > ES still has to talk to exactly the same number of shards for your > > query. The fact that there are more of them to choose from doesn't > > affect your query speed. > > > Where it will make a difference is when you reach the point that your 1 > > replica setup is too busy to cope with all of your queries. At that > > stage, having more replicas to choose from will help you to scale > > > clint ---
**Author:** ![Berkay\_Mollamustafao](https://avatars.discourse-cdn.com/v4/letter/b/22d042/32.png) [@Berkay\_Mollamustafao](https://discuss.elastic.co/u/Berkay_Mollamustafao)\ **Post date:** [January 9, 2012, 4:01pm UTC](https://discuss.elastic.co/t/number-of-replicas-and-query-speed/6321/5 "2012-01-09T16:01:20Z")
Can you give the details of the tests you're running? What are the variables in your tests? What resource (CPU, Disk IO, etc.) seems to be the bottleneck? How many client connections do you use? Do you increase the number? Do the clients run on the same box with servers? Which language is the client written in, could it be the bottleneck? What are the queries? do you change the queries or run the same ones? Are you only querying or updating the indices at the same time as well? It's not feasible to guess what the reason may be without fully understanding details of the tests. Regards, Berkay Mollamustafaoglu mberkay on yahoo, google and skype On Mon, Jan 9, 2012 at 10:50 AM, [bogdanionescu3@yahoo.com](mailto:bogdanionescu3@yahoo.com) wrote: > I did some tests under heavier load and I still could not see any > improvement when using more replicas... > > On Jan 9, 12:55 pm, [bogdaniones...@yahoo.com](mailto:bogdaniones...@yahoo.com) wrote: > > > I see... I agree the response time should be the same, but the I > > thought the throughput should increase. > > I'll try to increase the load and compare the results then. > > > > On Jan 9, 12:25 pm, Clinton Gormley [cl...@traveljury.com](mailto:cl...@traveljury.com) wrote: > > > > > Hiya > > > > > > I have a 4 node cluster with 7.7M docs indexed. 5 shards. > > > > Fist I've tried with 1 replica (default config) and we tested the > > > > query speed. It worked fine. > > > > The we used the REST API to increase the number of replicas to 4 and > > > > after a while the nodes reflected this change (in shards dirs stored > > > > locally all had a copy of all the 5 shards). > > > > The problems is that the query speed was exactly the same as when > > > > using 1 replica config! > > > > Any ideas why this happens? Shouldn't be any improvement at all? > > > > > ES still has to talk to exactly the same number of shards for your > > > query. The fact that there are more of them to choose from doesn't > > > affect your query speed. > > > > > Where it will make a difference is when you reach the point that your 1 > > > replica setup is too busy to cope with all of your queries. At that > > > stage, having more replicas to choose from will help you to scale > > > > > clint ---
**Author:** ![kimchy](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/kimchy/32/44952_2.png) [@kimchy](https://discuss.elastic.co/u/kimchy)\ **Post date:** [January 9, 2012, 7:49pm UTC](https://discuss.elastic.co/t/number-of-replicas-and-query-speed/6321/6 "2012-01-09T19:49:43Z")
On a 4 node setup with 5 shards and 1 replica increasing the number of replicas will not change the search performance, since all the nodes are already "maxed" in terms of search being executed on them. You are just "making" more shards, but you still have only 4 boxes. If you have an index that is already spread out, lets say an index with 2 shards and 1 replica on a 10 box cluster (there might be other indices), then increasing the number of replicas will help then, since you will span more boxes in this case. On Mon, Jan 9, 2012 at 5:50 PM, [bogdanionescu3@yahoo.com](mailto:bogdanionescu3@yahoo.com) wrote: > I did some tests under heavier load and I still could not see any > improvement when using more replicas... > > On Jan 9, 12:55 pm, [bogdaniones...@yahoo.com](mailto:bogdaniones...@yahoo.com) wrote: > > > I see... I agree the response time should be the same, but the I > > thought the throughput should increase. > > I'll try to increase the load and compare the results then. > > > > On Jan 9, 12:25 pm, Clinton Gormley [cl...@traveljury.com](mailto:cl...@traveljury.com) wrote: > > > > > Hiya > > > > > > I have a 4 node cluster with 7.7M docs indexed. 5 shards. > > > > Fist I've tried with 1 replica (default config) and we tested the > > > > query speed. It worked fine. > > > > The we used the REST API to increase the number of replicas to 4 and > > > > after a while the nodes reflected this change (in shards dirs stored > > > > locally all had a copy of all the 5 shards). > > > > The problems is that the query speed was exactly the same as when > > > > using 1 replica config! > > > > Any ideas why this happens? Shouldn't be any improvement at all? > > > > > ES still has to talk to exactly the same number of shards for your > > > query. The fact that there are more of them to choose from doesn't > > > affect your query speed. > > > > > Where it will make a difference is when you reach the point that your 1 > > > replica setup is too busy to cope with all of your queries. At that > > > stage, having more replicas to choose from will help you to scale > > > > > 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, 3:43am UTC](https://discuss.elastic.co/t/number-of-replicas-and-query-speed/6321/7 "2017-07-06T03:43:19Z")