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


ShardRouting failed to invoke before shard created callback
Could not remove routing entries for removed or shutting down nodes
%s model routing info was updated with %s and master notified
%s failed to update model routing info with %s
Low disk watermark exceeded on replicas will not be assigned to this node
Cluster info unavailable for disk threshold decider allowing allocation
Flood stage disk watermark exceeded on
Resetting current desired balance
%s deployment routing info was updated with %s and master notified
%s failed to update deployment routing info with %s
After allocating node would have less than the required free bytes threshold bytes free preventing allocation
After allocating node would have more than the allowed free disk threshold free preventing allocation

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