Briefly, this error occurs when Elasticsearch’s status is set to “S s”, which means it’s in a “shard started” state. This is not an error but a status message indicating that a shard has been successfully started. However, if you’re experiencing issues, it could be due to a misconfiguration or a problem with the cluster’s health. To resolve this, ensure that your cluster is properly configured, check the health of your cluster, and ensure that all nodes are functioning correctly. If the problem persists, consider reindexing your data or increasing the number of shards.
This guide will help you check for common problems that cause the log ” [%s] %s ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: replication.
Overview
Replication refers to storing a redundant copy of the data. Starting from version 7.x, Elasticsearch creates one primary shard with a replication factor set to 1. Replicas never get assigned to the same node on which primary shards are assigned, which means you should have at least two nodes in the cluster to assign the replicas. If a primary shard goes down, the replica automatically acts as a primary shard.
What it is used for
Replicas are used to provide high availability and failover. A higher number of replicas is also helpful for faster searches.
Examples
Update replica count
PUT /api-logs/_settings?pretty
{
"index" : {
"number_of_replicas" : 2
}
}Common problems
- By default, new replicas are not assigned to nodes with more than 85% disk usage. Instead, Elasticsearch throws a warning.
- Creating too many replicas may cause a problem if there are not enough resources available in the cluster.
Log Context
Log “[%s] %s” classname is TransportWriteAction.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
String message;
Exception exception;
ActionListener listener
) {
if (TransportActions.isShardNotAvailableException(exception) == false) {
logger.warn(() -> format("[%s] %s"; replica.shardId(); message); exception);
}
shardStateAction.remoteShardFailed(
replica.shardId();
replica.allocationId().getId();
primaryTerm;
