Briefly, this error occurs when Elasticsearch is unable to write metadata due to a blockage, often caused by a full disk or a read-only index. To resolve this issue, you can free up disk space or increase the disk capacity. If the index is read-only, you can update the index settings to allow writes. Additionally, check for any ongoing operations that might be blocking metadata writes and resolve them.
This guide will help you check for common problems that cause the log ” waiting until metadata writes are unblocked ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin, metadata.
Overview
Metadata in Elasticsearch refers to additional information stored for each document. This is achieved using the specific metadata fields available in Elasticsearch. The default behavior of some of these metadata fields can be customized during mapping creation.
Examples
Using _meta meta-field for storing application-specific information with the mapping:
PUT /my_index?pretty
{
"mappings": {
"_meta": {
"domain": "security",
"release_information": {
"date": "18-01-2020",
"version": "7.5"
}
}
}
}Notes
- In version 2.x, Elasticsearch had a total 13 meta fields available, which are: _index, _uid, _type, _id, _source, _size, _all, _field_names, _timestamp, _ttl, _parent, _routing, _meta
- In version 5.x, _timestamp and _ttl meta fields were removed.
- In version 6.x, the _parent meta field was removed.
- In version 7.x, _uid and _all meta fields were removed.
Log Context
Log “waiting until metadata writes are unblocked” class name is LocalExporter.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
ClusterState clusterState = clusterService.state();
if (clusterState.nodes().isLocalNodeElectedMaster()) {
// we are on the elected master
// Check that there is nothing that could block metadata updates
if (clusterState.blocks().hasGlobalBlockWithLevel(ClusterBlockLevel.METADATA_WRITE)) {
throw new ElasticsearchException("waiting until metadata writes are unblocked");
} // We haven't blocked off other resource installation from happening. That must be done first.
assert migrationCoordinator.canInstall() == false : "migration attempted while resources could be erroneously installed";
