# How to correctly determine the weight of a node

**URL:** <https://discuss.elastic.co/t/how-to-correctly-determine-the-weight-of-a-node/224871>\
**Category:** Elasticsearch\
**Created:** [March 24, 2020, 3:31pm UTC](https://discuss.elastic.co/t/how-to-correctly-determine-the-weight-of-a-node/224871 "2020-03-24T15:31:31Z")\
**Posts on this page:** 1\
**Showing post:** 3

<div class="post-metadata">

**Author:** ![Paul\_Le\_Tilly](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/paul_le_tilly/32/97836_2.png) [@Paul\_Le\_Tilly](https://discuss.elastic.co/u/Paul_Le_Tilly)\
**Post date:** [March 2, 2023, 9:59am UTC](https://discuss.elastic.co/t/how-to-correctly-determine-the-weight-of-a-node/224871/3 "2023-03-02T09:59:41Z")

</div>

Hey there,

I was wondering the same thing, and went on a little trip into [the rabbit hole](https://github.com/elastic/elasticsearch/blob/8bcecec21788b8100ecf576cf83086c6d68bfc02/server/src/main/java/org/elasticsearch/cluster/routing/allocation/allocator/BalancedShardsAllocator.java#L287).

There you have the code for the WeightFunction class that compute the weight of each nodes.

And as you can see the [weight function](https://github.com/elastic/elasticsearch/blob/8bcecec21788b8100ecf576cf83086c6d68bfc02/server/src/main/java/org/elasticsearch/cluster/routing/allocation/allocator/BalancedShardsAllocator.java#L305) does the computation on 4 characteristics of a node:

- ShardsLoad = Number of shard on the node - Avg number of shards per node in the cluster
- IndexLoad = Number of shard for a given index - Avg number of shards for a given index in the cluster
- WriteLoad = [Write load on a node](https://github.com/elastic/elasticsearch/blob/8bcecec21788b8100ecf576cf83086c6d68bfc02/server/src/main/java/org/elasticsearch/cluster/routing/allocation/allocator/BalancedShardsAllocator.java#L1311) - Avg write load
- DiskLoad = [Actual disk usage](https://github.com/elastic/elasticsearch/blob/8bcecec21788b8100ecf576cf83086c6d68bfc02/server/src/main/java/org/elasticsearch/cluster/routing/allocation/allocator/BalancedShardsAllocator.java#L1312) - Avg disk usage in the cluster

All of those are then multiplied by [their respective settings](https://www.elastic.co/guide/en/elasticsearch/reference/master/modules-cluster.html#shards-rebalancing-heuristics) and divided by the sum of all settings.

SumSettings = `cluster.routing.allocation.balance.shard` + `cluster.routing.allocation.balance.index` + `cluster.routing.allocation.balance.disk_usage` + `cluster.routing.allocation.balance.write_load`

So in the end you have:

Weight = ShardsLoad \* `cluster.routing.allocation.balance.shard` / SumSettings  
+ IndexLoad \* `cluster.routing.allocation.balance.index` / SumSettings  
+ WriteLoad \* `cluster.routing.allocation.balance.write_load` / SumSettings  
+ DiskLoad \* `cluster.routing.allocation.balance.disk_usage` / SumSettings

---

_[View the full topic](https://discuss.elastic.co/t/how-to-correctly-determine-the-weight-of-a-node/224871)._