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Briefly, this error occurs when a required property in your OpenSearch configuration or query is set to null, which is not allowed. This could be due to a missing field in the data being indexed or a null value in a query. To resolve this, ensure all required fields are present in your data and that no null values are used in queries. If the error persists, check your OpenSearch configuration for any properties that may be incorrectly set to null.
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This guide will help you check for common problems that cause the log ” Property [null_value] cannot be null. ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: index, plugins.
Quick links
Overview
In OpenSearch, an index (plural: indices) contains a schema and can have one or more shards and replicas. An OpenSearch index is divided into shards and each shard is an instance of a Lucene index.
Indices are used to store the documents in dedicated data structures corresponding to the data type of fields. For example, text fields are stored inside an inverted index whereas numeric and geo fields are stored inside BKD trees.
Examples
Create index
The following example is based on OpenSearch version 5.x onwards. An index with two shards, each having one replica will be created with the name test_index1
PUT /test_index1?pretty
{
"settings" : {
"number_of_shards" : 2,
"number_of_replicas" : 1
},
"mappings" : {
"properties" : {
"tags" : { "type" : "keyword" },
"updated_at" : { "type" : "date" }
}
}
}List indices
All the index names and their basic information can be retrieved using the following command:
GET _cat/indices?v
Index a document
Let’s add a document in the index with the command below:
PUT test_index1/_doc/1
{
"tags": [
"opster",
"OpenSearch"
],
"date": "01-01-2020"
}Query an index
GET test_index1/_search
{
"query": {
"match_all": {}
}
}Query multiple indices
It is possible to search multiple indices with a single request. If it is a raw HTTP request, index names should be sent in comma-separated format, as shown in the example below, and in the case of a query via a programming language client such as python or Java, index names are to be sent in a list format.
GET test_index1,test_index2/_search
Delete indices
DELETE test_index1
Common problems
- It is good practice to define the settings and mapping of an Index wherever possible because if this is not done, OpenSearch tries to automatically guess the data type of fields at the time of indexing. This automatic process may have disadvantages, such as mapping conflicts, duplicate data and incorrect data types being set in the index. If the fields are not known in advance, it’s better to use dynamic index templates.
- OpenSearch supports wildcard patterns in Index names, which sometimes aids with querying multiple indices, but can also be very destructive too. For example, It is possible to delete all the indices in a single command using the following commands:
DELETE /*
To disable this, you can add the following lines in the OpenSearch.yml:
action.destructive_requires_name: true
Overview
A plugin is used to enhance the core functionalities of OpenSearch. OpenSearch provides some core plugins as a part of their release installation. In addition to those core plugins, it is possible to write your own custom plugins as well. There are several community plugins available on GitHub for various use cases.
Examples
Get all of the instructions for the plugin:
sudo bin/opensearch-plugin -h
Installing the S3 plugin for storing OpenSearch snapshots on S3:
sudo bin/opensearch-plugin install repository-s3
Removing a plugin:
sudo bin/opensearch-plugin remove repository-s3
Installing a plugin using the file’s path:
sudo bin/opensearch-plugin install file:///path/to/plugin.zip
Notes and good things to know
- Plugins are installed and removed using the opensearch-plugin script, which ships as a part of the OpenSearch installation and can be found inside the bin/ directory of the OpenSearch installation path.
- A plugin has to be installed on every node of the cluster and each of the nodes has to be restarted to make the plugin visible.
- You can also download the plugin manually and then install it using the opensearch-plugin install command, providing the file name/path of the plugin’s source file.
- When a plugin is removed, you will need to restart every OpenSearch node in order to complete the removal process.
Common issues
- Managing permission issues during and after plugin installation is the most common problem. If OpenSearch was installed using the DEB or RPM packages then the plugin has to be installed using the root user. Otherwise you can install the plugin as the user that owns all of the OpenSearch files.
- In the case of DEB or RPM package installation, it is important to check the permissions of the plugins directory after you install it. You can update the permission if it has been modified using the following command:
chown -R opensearch:opensearch path_to_plugin_directory
- If your OpenSearch nodes are running in a private subnet without internet access, you cannot install a plugin directly. In this case, you can simply download the plugins and copy the files inside the plugins directory of the OpenSearch installation path on every node. The node has to be restarted in this case as well.
Log Context
Log “Property [null_value] cannot be null.” class name is ICUCollationKeywordFieldMapper.java. We extracted the following from OpenSearch source code for those seeking an in-depth context :
String fieldName = entry.getKey();
Object fieldNode = entry.getValue();
switch (fieldName) {
case "null_value":
if (fieldNode == null) {
throw new MapperParsingException("Property [null_value] cannot be null.");
}
builder.nullValue(fieldNode.toString());
iterator.remove();
break;
case "ignore_above":
