# Limited read and write speed using Elasticsearch Hadoop

**URL:** <https://discuss.elastic.co/t/limited-read-and-write-speed-using-elasticsearch-hadoop/314180>\
**Category:** Elasticsearch\
**Tags:** es-hadoop\
**Created:** [September 12, 2022, 10:19am UTC](https://discuss.elastic.co/t/limited-read-and-write-speed-using-elasticsearch-hadoop/314180 "2022-09-12T10:19:26Z")\
**Posts on this page:** 1\
**Showing post:** 7

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**Author:** ![Thijsvdp](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/thijsvdp/32/146696_2.png) [@Thijsvdp](https://discuss.elastic.co/u/Thijsvdp)\
**Post date:** [September 13, 2022, 8:27am UTC](https://discuss.elastic.co/t/limited-read-and-write-speed-using-elasticsearch-hadoop/314180/7 "2022-09-13T08:27:25Z")

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@Keith_Massey Yeah I am sorry for the confusion.

I am curious though about the relationship between shards and CPU. According to the [documentation](https://www.elastic.co/guide/en/elasticsearch/reference/current/size-your-shards.html#single-thread-per-shard) and some other [discussions](https://discuss.elastic.co/t/higher-cpu-vs-higher-memory-which-helps-in-what-cases/272798/23) each shard runs a search on a single thread. Does this mean that if you have, say 6 shards and 12 threads/vCPU available, it only uses 6/12 threads? Or can it use multiple per shard?

And what is the relation between shards and CPU for writing? Say I have 6 shards, and 12 threads/vCPU available, can I write using 12 Spark tasks? Or will that be useless and overload the cluster?

And last question, what is the relationship between RAM available and shard size?

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