Briefly, this error occurs when Elasticsearch expects a start object but doesn’t find one. This is usually due to a malformed request or incorrect data format. To resolve this, ensure that your request is correctly formatted, typically as a JSON object. Also, check that the INDEX_METADATA_IDENTIFIERS are correctly defined and used. If you’re using a client library to interact with Elasticsearch, ensure it’s up-to-date and compatible with your Elasticsearch version.
This guide will help you check for common problems that cause the log ” start object expected [” + INDEX_METADATA_IDENTIFIERS + “] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: repositories.
Overview
An Elasticsearch snapshot provides a backup mechanism that takes the current state and data in the cluster and saves it to a repository (read snapshot for more information). The backup process requires a repository to be created first. The repository needs to be registered using the _snapshot endpoint, and multiple repositories can be created per cluster. The following repository types are supported:
Repository types
| Repository type | Configuration type |
|---|---|
| Shared file system | Type: “fs” |
| S3 | Type : “s3” |
| HDFS | Type :“hdfs” |
| Azure | Type: “azure” |
| Google Cloud Storage | Type : “gcs” |
Examples
To register an “fs” repository:
PUT _snapshot/my_repo_01
{
"type": "fs",
"settings": {
"location": "/mnt/my_repo_dir"
}
}Notes and good things to know
- S3, HDFS, Azure and Google Cloud require a relevant plugin to be installed before it can be used for a snapshot.
- The setting, path.repo: /mnt/my_repo_dir needs to be added to elasticsearch.yml on all the nodes if you are planning to use the repo type of file system. Otherwise, it will fail.
- When using remote repositories, the network bandwidth and repository storage throughput should be high enough to complete the snapshot operations normally, otherwise you will end up with partial snapshots.
Log Context
Log “start object expected [” + INDEX_METADATA_IDENTIFIERS + “]” class name is RepositoryData.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
}
}
}
} else if (INDEX_METADATA_IDENTIFIERS.equals(field)) {
if (parser.nextToken() != XContentParser.Token.START_OBJECT) {
throw new ElasticsearchParseException("start object expected [" + INDEX_METADATA_IDENTIFIERS + "]");
}
indexMetaIdentifiers.putAll(parser.mapStrings());
} else if (MIN_VERSION.equals(field)) {
if (parser.nextToken() != XContentParser.Token.VALUE_STRING) {
throw new ElasticsearchParseException("version string expected [min_version]");
