Briefly, this error occurs when Elasticsearch expects an array to start but doesn’t find it. It’s usually due to incorrect JSON formatting in the request body, specifically related to the “snapshots” field. To resolve this, ensure that the “snapshots” field is correctly formatted as an array. If it’s a single snapshot, it should still be enclosed in square brackets. Also, check for any missing or extra commas, brackets, or quotation marks in your JSON request.
This guide will help you check for common problems that cause the log ” start array expected [snapshots] ” 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 array expected [snapshots]” class name is RepositoryData.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
parser.nextToken();
if (INDEX_ID.equals(indexMetaFieldName)) {
indexId = new IndexId(indexName; parser.text());
} else if (SNAPSHOTS.equals(indexMetaFieldName)) {
if (parser.currentToken() != XContentParser.Token.START_ARRAY) {
throw new ElasticsearchParseException("start array expected [snapshots]");
}
while (parser.nextToken() != XContentParser.Token.END_ARRAY) {
String uuid = null;
// the old format pre 5.4.1 which contains the snapshot name and uuid
if (parser.currentToken() == XContentParser.Token.START_OBJECT) {
[ratemypost]
