Briefly, this error occurs when Elasticsearch tries to remove a read-only block due to a failed reindex operation. This could be due to insufficient disk space, incorrect index settings, or network issues. To resolve this, you can free up disk space, check and correct your index settings, or troubleshoot your network. Additionally, ensure that your Elasticsearch cluster has enough resources to handle the reindex operation.
This guide will help you check for common problems that cause the log ” removing read only block on [{}] because reindex failed [{}] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: reindex.
Overview
Reindex is the concept of copying existing data from a source index to a destination index which can be inside the same or a different cluster. Elasticsearch has a dedicated endpoint _reindex for this purpose. A reindexing is mostly required for updating mapping or settings.
Examples
Reindex data from a source index to destination index in the same cluster:
POST /_reindex?pretty
{
"source": {
"index": "news"
},
"dest": {
"index": "news_v2"
}
}
Notes
- Reindex API does not copy settings and mappings from the source index to the destination index. You need to create the destination index with the desired settings and mappings before you begin the reindexing process.
- The API exposes an extensive list of configuration options to fetch data from the source index, such as query-based indexing and selecting multiple indices as the source index.
- In some scenarios reindex API is not useful, where reindexing requires complex data processing and data modification based on application logic. In this case, you can write your custom script using Elasticsearch scroll API to fetch the data from source index and bulk API to index data into destination index.
Log Context
Log “removing read only block on [{}] because reindex failed [{}]” classname is SystemIndexMigrator.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
migrationInfo.createClient(baseClient).execute(ReindexAction.INSTANCE; reindexRequest; listener);
}
// Failure handlers
private void removeReadOnlyBlockOnReindexFailure(Index index; ActionListener listener; Exception ex) {
logger.info("removing read only block on [{}] because reindex failed [{}]"; index; ex);
setWriteBlock(index; false; ActionListener.wrap(unsetReadOnlyResponse -> listener.onFailure(ex); e1 -> listener.onFailure(ex)));
}
private static ElasticsearchException logAndThrowExceptionForFailures(BulkByScrollResponse bulkByScrollResponse) {
String bulkFailures = (bulkByScrollResponse.getBulkFailures() != null)
