Elasticsearch Routing

By Opster Team

Updated: Mar 21, 2023

| 1 min read

Overview

In Elasticsearch, routing refers to document routing. When you index a document, Elasticsearch will determine which shard the document should be routed to for indexing

The shard is selected based on the following formula:

shard = hash(_routing) % number_of_primary_shards

Where the default value of _routing is _id.
It is important to know which shard the document is routed to, because Elasticsearch will need to determine where to find that document later on for document retrieval requests. 

Examples

In twitter index with 2 primary shards, the document with _id equal to “440” gets routed to the shard number:   

shard = hash( 440 ) % 2
PUT twitter/_doc/440
{
...
}

Notes and good things to know

  • In order to improve search speed, you can create custom routing. For example, you can enable custom routing that will ensure that only a single shard will be queried (the shard that contains your data).
  • To create custom routing in Elasticsearch, you will need to configure and define that not all routing will be completed by default settings. ( v <= 5.0)
PUT my_index/customer/_mapping
{
   "order":{
      "_routing":{
         "required":true
      }
   }
}
  •  This will ensure that every document in the “customer” type must specify a custom routing. For Elasticsearch version 6 or above you will need to update the same mapping as:
PUT my_index/_mapping
{
   "order":{
      "_routing":{
         "required":true
      }
   }
}

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Related log errors to this ES concept


Delaying allocation for unassigned shards next check in
Updating cluster routing allocation awareness attributes from to
Updating cluster routing allocation cluster concurrent rebalance from to
Updating cluster routing allocation disable allocation from to
Updating cluster routing allocation disable new allocation from to
Updating cluster routing allocation disable replica allocation from to
Updating cluster routing allocation node concurrent recoveries from to
Updating cluster routing allocation node initial primaries recoveries from to
After allocating node would have less than the required free disk threshold free preventing allocation
Cluster routing allocation allow rebalance has a wrong value defaulting to indices all active
Failed to get parse meta for
High disk watermark exceeded on one or more nodes rerouting shards

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