Documentation for configurable merge policy

Signed-off-by: Rishabh Maurya <[email protected]>

_api-reference/cluster-api/cluster-settings.md

@@ -114,7 +114,7 @@ The following request field parameters are compatible with the cluster API.
 | cluster.persistent_tasks.allocation.enable | String | Enables or disables allocation for persistent tasks: <br /> <br /> `all` – Allows persistent tasks to be assigned to nodes. <br /> <br /> `none` – No allocations are allowed for persistent tasks. This does not affect persistent tasks already running. <br /> <br /> Default is `all`. |
 | cluster.persistent_tasks.allocation.recheck_interval | Time unit | The cluster manager automatically checks whether or not persistent tasks need to be assigned when the cluster state changes in a significant way. There are other factors, such as memory usage, that will affect whether or not persistent tasks are assigned to nodes but do not otherwise cause the cluster state to change. This setting defines how often assignment checks are performed in response to these factors. Default is `30 seconds`, with a minimum of `10 seconds` being required. |
 | remote_store.moving_average_window_size | Integer | The moving average window size used to calculate the rolling statistic values exposed through the [Remote Store Stats API]({{site.url}}{{site.baseurl}}/tuning-your-cluster/availability-and-recovery/remote-store/remote-store-stats-api/). Default is `20`. Minimum enforced is `5`. |
-
+| indices.time_series_index.default_index_merge_policy| String | This setting allows to specify the default merge policy for time-series indices, particularly those with a `@timestamp` field such as datastreams. The two available options are: `tiered` (default) and `log_byte_size`. `log_byte_size` is recommended for time-series indices to enhance performance on range queries on `@timestamp` field. To override the merge policy on a per-index basis, the `index.merge.policy` index setting can be used. |
 
 #### Example request
 
@@ -144,4 +144,4 @@ For more information about transient settings, persistent settings, and preceden
    },
    "transient":{}
 }
-```
+```

_im-plugin/index-settings.md

@@ -42,6 +42,7 @@ index.routing_partition_size | The number of shards a custom routing value can g
 index.soft_deletes.retention_lease.period | The maximum amount of time to retain a shard's history of operations. Default is `12h`.
 index.load_fixed_bitset_filters_eagerly | Whether OpenSearch should preload cached filters. Available options are `true` and `false`. Default is `true`.
 index.hidden | Whether the index should be hidden. Hidden indexes are not returned as part of queries that have wildcards. Available options are `true` and `false`. Default is `false`.
+index.merge.policy | This setting controls the merge policy for the lucene segments. Available options are `tiered` and `log_byte_size`. Default is `tiered`. However, for time-series data, such as log events, it is advisable to switch to the `log_byte_size` merge policy. This can improve the query performance when conducting range queries on the `@timestamp` field.  It is advisable not to change the merge policy of an existing index. Instead, configure this setting when creating a new index.
 
 ## Updating a static index setting