Briefly, this error occurs when Elasticsearch detects an index that is not referenced in the cluster state. This is known as a “dangled” index. It happens due to abrupt shutdown or data node failures. Elasticsearch tries to recover by renaming the directory. To resolve this, ensure proper shutdown procedures are followed to prevent data loss. Regularly monitor your cluster’s health and handle node failures promptly. Also, consider setting the ‘gateway.recover_after_nodes’ property to control the recovery process of dangled indices. Lastly, ensure your Elasticsearch version is up-to-date as newer versions have better error handling.
This guide will help you check for common problems that cause the log ” dangled index directory name is [{}]; state name is [{}]; renaming to directory name ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: dangled, dangling, index and indices.
Overview
In Elasticsearch, an index (plural: indices) contains a schema and can have one or more shards and replicas. An Elasticsearch index is divided into shards and each shard is an instance of a Lucene index.
Indices are used to store the documents in dedicated data structures corresponding to the data type of fields. For example, text fields are stored inside an inverted index whereas numeric and geo fields are stored inside BKD trees.
Examples
Create index
The following example is based on Elasticsearch version 5.x onwards. An index with two shards, each having one replica will be created with the name test_index1
PUT /test_index1?pretty
{
"settings" : {
"number_of_shards" : 2,
"number_of_replicas" : 1
},
"mappings" : {
"properties" : {
"tags" : { "type" : "keyword" },
"updated_at" : { "type" : "date" }
}
}
}List indices
All the index names and their basic information can be retrieved using the following command:
GET _cat/indices?v
Index a document
Let’s add a document in the index with the command below:
PUT test_index1/_doc/1
{
"tags": [
"opster",
"elasticsearch"
],
"date": "01-01-2020"
}Query an index
GET test_index1/_search
{
"query": {
"match_all": {}
}
}Query multiple indices
It is possible to search multiple indices with a single request. If it is a raw HTTP request, index names should be sent in comma-separated format, as shown in the example below, and in the case of a query via a programming language client such as python or Java, index names are to be sent in a list format.
GET test_index1,test_index2/_search
Delete indices
DELETE test_index1
Common problems
- It is good practice to define the settings and mapping of an Index wherever possible because if this is not done, Elasticsearch tries to automatically guess the data type of fields at the time of indexing. This automatic process may have disadvantages, such as mapping conflicts, duplicate data and incorrect data types being set in the index. If the fields are not known in advance, it’s better to use dynamic index templates.
- Elasticsearch supports wildcard patterns in Index names, which sometimes aids with querying multiple indices, but can also be very destructive too. For example, It is possible to delete all the indices in a single command using the following commands:
DELETE /*
To disable this, you can add the following lines in the elasticsearch.yml:
action.destructive_requires_name: true
Log Context
Log “dangled index directory name is [{}]; state name is [{}]; renaming to directory name” classname is DanglingIndicesState.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
try {
IndexMetaData indexMetaData = metaStateService.loadIndexState(indexName);
if (indexMetaData != null) {
logger.info("[{}] dangling index; exists on local file system; but not in cluster metadata; auto import to cluster state"; indexName);
if (!indexMetaData.getIndex().equals(indexName)) {
logger.info("dangled index directory name is [{}]; state name is [{}]; renaming to directory name"; indexName; indexMetaData.getIndex());
indexMetaData = IndexMetaData.builder(indexMetaData).index(indexName).build();
}
newIndices.put(indexName; indexMetaData);
} else {
logger.debug("[{}] dangling index directory detected; but no state found"; indexName);
