Merge branch 'main' into hdhalter-patch-28

.github/vale/styles/Vocab/OpenSearch/Words/accept.txt

@@ -123,6 +123,7 @@ stdout
 [Ss]ubvector
 [Ss]ubwords?
 [Ss]uperset
+[Ss]yslog
 tebibyte
 [Tt]emplated
 [Tt]okenization

TERMS.md

@@ -236,6 +236,8 @@ Do not use *disable* to refer to users.
 
 Always hyphenated. Don’t use _double click_.
 
+**downvote**
+
 **dropdown list**
 
 **due to**
@@ -586,6 +588,10 @@ Use % in headlines, quotations, and tables or in technical copy.
 
 An agent and REST API that allows you to query numerous performance metrics for your cluster, including aggregations of those metrics, independent of the Java Virtual Machine (JVM).
 
+**plaintext, plain text**
+
+Use *plaintext* only to refer to nonencrypted or decrypted text in content about encryption. Use *plain text* to refer to ASCII files.
+
 **please**
 
 Avoid using except in quoted text.
@@ -700,6 +706,8 @@ Never hyphenated. Use _startup_ as a noun (for example, “The following startup
 
 **Stochastic Gradient Descent (SGD)**
 
+**syslog**
+
 ## T
 
 **term frequency–inverse document frequency (TF–IDF)**
@@ -746,6 +754,8 @@ A storage tier that you can use to store and analyze your data with Elasticsearc
 
 Hyphenate as adjectives. Use instead of *top left* and *top right*, unless the field name uses *top*. For example, "The upper-right corner."
 
+**upvote**
+
 **US**
 
 No periods, as specified in the Chicago Manual of Style.

_dashboards/dashboards-assistant/index.md

@@ -60,7 +60,7 @@ For information about configuring OpenSearch Assistant through the REST API, see
 
 ## Using OpenSearch Assistant in OpenSearch Dashboards
 
-The following tutorials guide you through using OpenSearch Assistant in OpenSearch Dashboards. OpenSearch Assistant can be viewed full frame or in the right sidebar. The default is sidebar. To view full frame, select the frame icon {::nomarkdown}<img src="{{site.url}}{{site.baseurl}}/images/icons/frame-icon.png" class="inline-icon" alt="frame icon"/>{:/} in the toolbar. 
+The following tutorials guide you through using OpenSearch Assistant in OpenSearch Dashboards. OpenSearch Assistant can be viewed in full frame or in the sidebar. The default view is in the right sidebar. To view the assistant in the left sidebar or in full frame, select the {::nomarkdown}<img src="{{site.url}}{{site.baseurl}}/images/icons/frame-icon.png" class="inline-icon" alt="frame icon"/>{:/} icon in the toolbar and choose the preferred option. 
 
 ### Start a conversation
 

_dashboards/management/index-patterns.md

@@ -56,7 +56,7 @@ An example of step 1 is shown in the following image. Note that the index patter
 
 Once the index pattern has been created, you can view the mapping of the matching indexes. Within the table, you can see the list of fields, along with their data type and properties. An example is shown in the following image.
 
-<img src="{{site.url}}{{site.baseurl}}//images/dashboards/index-pattern-table.png" alt="Index pattern table UI " width="700"/>
+<img src="{{site.url}}{{site.baseurl}}/images/dashboards/index-pattern-table.png" alt="Index pattern table UI " width="700"/>
 
 ## Next steps
 

_install-and-configure/configuring-opensearch/index-settings.md

@@ -100,6 +100,7 @@ OpenSearch supports the following static index-level index settings:
 
 - `index.merge_on_flush.policy` (default | merge-on-flush): This setting controls which merge policy should be used when `index.merge_on_flush.enabled` is enabled. Default is `default`.
 
+- `index.check_pending_flush.enabled` (Boolean): This setting controls the Apache Lucene `checkPendingFlushOnUpdate` index writer setting, which specifies whether an indexing thread should check for pending flushes on an update in order to flush indexing buffers to disk. Default is `true`.
 
 ### Updating a static index setting
 

_search-plugins/caching/index.md

@@ -0,0 +1,32 @@
+---
+layout: default
+title: Caching
+parent: Improving search performance
+has_children: true
+nav_order: 100
+---
+
+# Caching
+
+OpenSearch relies heavily on different on-heap cache types to accelerate data retrieval, providing significant improvement in search latencies. However, cache size is limited by the amount of memory available on a node. If you are processing a larger dataset that can potentially be cached, the cache size limit causes a lot of cache evictions and misses. The increasing number of evictions impacts performance because OpenSearch needs to process the query again, causing high resource consumption.
+
+Prior to version 2.13, OpenSearch supported the following on-heap cache types:
+
+- **Request cache**: Caches the local results on each shard. This allows frequently used (and potentially resource-heavy) search requests to return results almost instantly. 
+- **Query cache**: The shard-level query cache caches common data from similar queries. The query cache is more granular than the request cache and can cache data that is reused in different queries.
+- **Field data cache**: The field data cache contains field data and global ordinals, which are both used to support aggregations on certain field types.
+
+## Additional cache stores
+**Introduced 2.13**
+{: .label .label-purple }
+
+This is an experimental feature and is not recommended for use in a production environment. For updates on the progress of the feature or if you want to leave feedback, see the associated [GitHub issue](https://github.com/opensearch-project/OpenSearch/issues/10024).    
+{: .warning}
+
+In addition to existing OpenSearch custom on-heap cache stores, cache plugins provide the following cache stores: 
+
+- **Disk cache**: This cache stores the precomputed result of a query on disk. You can use a disk cache to cache much larger datasets, provided that the disk latencies are acceptable.
+- **Tiered cache**: This is a multi-level cache, in which each tier has its own characteristics and performance levels. For example, a tiered cache can contain on-heap and disk tiers. By combining different tiers, you can achieve a balance between cache performance and size. To learn more, see [Tiered cache]({{site.url}}{{site.baseurl}}/search-plugins/caching/tiered-cache/).
+
+In OpenSearch 2.13, the request cache is integrated with cache plugins. You can use a tiered or disk cache as a request-level cache.
+{: .note}

_search-plugins/caching/tiered-cache.md

@@ -0,0 +1,82 @@
+---
+layout: default
+title: Tiered cache
+parent: Caching
+grand_parent: Improving search performance
+nav_order: 10
+---
+
+# Tiered cache
+
+This is an experimental feature and is not recommended for use in a production environment. For updates on the progress of the feature or if you want to leave feedback, see the associated [GitHub issue](https://github.com/opensearch-project/OpenSearch/issues/10024).    
+{: .warning}
+
+A tiered cache is a multi-level cache, in which each tier has its own characteristics and performance levels. By combining different tiers, you can achieve a balance between cache performance and size.
+
+## Types of tiered caches
+
+OpenSearch 2.13 provides an implementation of _tiered spillover cache_. This implementation spills the evicted items from upper to lower tiers. The upper tier is smaller in size but offers better latency, like the on-heap tier. The lower tier is larger in size but is slower in terms of latency compared to the upper tier. A disk cache is an example of a lower tier. OpenSearch 2.13 offers on-heap and disk tiers. 
+
+## Enabling a tiered cache
+
+To enable a tiered cache, configure the following setting:
+
+```yaml
+opensearch.experimental.feature.pluggable.caching.enabled: true
+```
+{% include copy.html %}
+
+For more information about ways to enable experimental features, see [Experimental feature flags]({{site.url}}{{site.baseurl}}/install-and-configure/configuring-opensearch/experimental/).
+
+## Installing required plugins
+
+A tiered cache provides a way to plug in any disk or on-heap tier implementation. You can install the plugins you intend to use in the tiered cache. As of OpenSearch 2.13, the available cache plugin is the `cache-ehcache` plugin. This plugin provides a disk cache implementation to use within a tiered cache as a disk tier. 
+
+A tiered cache will fail to initialize if the `cache-ehcache` plugin is not installed or disk cache properties are not set.
+{: .warning}
+
+## Tiered cache settings
+
+In OpenSearch 2.13, a request cache can use a tiered cache. To begin, configure the following settings in the `opensearch.yml` file.
+
+### Cache store name
+
+Set the cache store name to `tiered_spillover` to use the OpenSearch-provided tiered spillover cache implementation:
+
+```yaml
+indices.request.cache.store.name: tiered_spillover: true
+```
+{% include copy.html %}
+
+### Setting on-heap and disk store tiers
+
+The `opensearch_onheap` setting is the built-in on-heap cache available in OpenSearch. The `ehcache_disk` setting is the disk cache implementation from [Ehcache](https://www.ehcache.org/). This requires installing the `cache-ehcache` plugin:
+
+```yaml
+indices.request.cache.tiered_spillover.onheap.store.name: opensearch_onheap
+indices.request.cache.tiered_spillover.disk.store.name: ehcache_disk
+```
+{% include copy.html %}
+
+For more information about installing non-bundled plugins, see [Additional plugins]({{site.url}}{{site.baseurl}}/install-and-configure/plugins/#additional-plugins).
+
+### Configuring on-heap and disk stores
+
+The following table lists the cache store settings for the `opensearch_onheap` store.
+
+Setting | Default | Description
+:--- | :--- | :---
+`indices.request.cache.opensearch_onheap.size` | 1% of the heap | The size of the on-heap cache. Optional.
+`indices.request.cache.opensearch_onheap.expire` | `MAX_VALUE` (disabled) | Specify a time-to-live (TTL) for the cached results. Optional.
+
+The following table lists the disk cache store settings for the `ehcache_disk` store.
+
+Setting | Default | Description
+:--- | :--- | :---
+`indices.request.cache.ehcache_disk.max_size_in_bytes` | `1073741824` (1 GB)  | Defines the size of the disk cache. Optional.
+`indices.request.cache.ehcache_disk.storage.path` | `""` | Defines the storage path for the disk cache. Required.
+`indices.request.cache.ehcache_disk.expire_after_access` | `MAX_VALUE` (disabled) | Specify a time-to-live (TTL) for the cached results. Optional.
+`indices.request.cache.ehcache_disk.alias` | `ehcacheDiskCache#INDICES_REQUEST_CACHE` (this is an example of request cache) | Specify an alias for the disk cache. Optional.
+`indices.request.cache.ehcache_disk.segments` | `16` | Defines the number of segments the disk cache is separated into. Used for concurrency. Optional.
+`indices.request.cache.ehcache_disk.concurrency` | `1` | Defines the number of distinct write queues created for the disk store, where a group of segments share a write queue. Optional.
+

_security/access-control/anonymous-authentication.md

@@ -30,6 +30,19 @@ The following table describes the `anonymous_auth_enabled` setting. For more inf
 If you disable anonymous authentication, you must provide at least one `authc` in order for the Security plugin to initialize successfully.
 {: .important }
 
+## OpenSearch Dashboards configuration
+
+To enable anonymous authentication for OpenSearch Dashboards, you need to modify the `opensearch_dashboards.yml` file in the configuration directory of your OpenSearch Dashboards installation.
+
+Add the following setting to `opensearch_dashboards.yml`:
+
+```yml
+opensearch_security.auth.anonymous_auth_enabled: true
+```
+
+Anonymous login for OpenSearch Dashboards requires anonymous authentication to be enabled on the OpenSearch cluster.
+{: .important}
+
 ## Defining anonymous authentication privileges
 
 When anonymous authentication is enabled, your defined HTTP authenticators still try to find user credentials inside your HTTP request. If credentials are found, the user is authenticated. If none are found, the user is authenticated as an `anonymous` user.