This status badge "passing" means that you still have to remember to set number_of_routing_shards AND routing_partition_size when creating the index in order to have equally distributed writes in OpenSearch.

This repo just contains a test script reproducing the last known behavior until the related issue is fixed in OpenSearch:

• OpenSearch #17472 - Index setting partition size is ignored if routing num shard setting is not specified

Also see:

• OpenSearch current documentation: Routing: Routing To Specific Shards
• Elasticsearch #48863 - Original Elasticsearch issue describing the same behavior from before the OpenSearch fork

When creating an index with:

• routing_partition_size: 2
• Required routing
• No number_of_routing_shards specified

All documents with the same routing value get assigned to the same shard, instead of being distributed across multiple shards as expected.

# run with opensearch 1, 2, 3 release (from tags: https://gallery.ecr.aws/opensearchproject/opensearch)
# have only tested so far with 1 or 2
./opensearch_routing_bug.sh 1

The script will:

• Check if OpenSearch is running locally
• Create two test indices:
  1. With number_of_routing_shards
  2. Without number_of_routing_shards
• Insert test documents with the same routing value
• Show shard distribution for both cases and assert whether the behavior has changed or not

Expected:

• Documents with the same routing value should be distributed across 2 shards (as specified by routing_partition_size)

Actual:

• With number_of_routing_shards: Documents are correctly distributed
• Without number_of_routing_shards: All documents go to the same shard