DOC-13173 Enhance documentation for Index Rebalance and Upgrade

modules/learn/pages/clusters-and-availability/failover.adoc

@@ -27,9 +27,9 @@ Graceful failover _must_ be manually initiated. Hard failover _can_ be manually
 Hard failover can also be initiated automatically by Couchbase Server: this is known as _automatic_ failover.
 The Cluster Manager detects the unavailability of a node, and duly initiates a _hard_ failover, without administrator intervention.
 
-
-Note that when a node is failed over (as opposed to _removed_), some replica vBuckets are lost from the surviving nodes; since some are promoted to _active_ status, and are not replaced with new replica-copies.
-By contrast, xref:learn:clusters-and-availability/removal.adoc[removal] creates new copies of those replica vBuckets that would otherwise be lost. This maintains the cluster's previous level of data-availability; but results in greater competition for memory resources, across the surviving nodes.
+NOTE: When a node is failed over (as opposed to _removed_), some replica vBuckets are lost from the surviving nodes; since some are promoted to _active_ status, and are not replaced with new replica-copies.
+By contrast, xref:learn:clusters-and-availability/removal.adoc[removal] creates new copies of those replica vBuckets that would otherwise be lost.
+This maintains the cluster's previous level of data-availability; but results in greater competition for memory resources, across the surviving nodes.
 
 Ideally, after any failover, xref:learn:clusters-and-availability/rebalance.adoc[rebalance] should be performed.
 This is especially important when a Data Service node has been failed over, since the rebalance will ensure an optimal ratio of active to replica vBuckets across all the remaining Data Service nodes.

modules/learn/pages/clusters-and-availability/rebalance.adoc

@@ -145,6 +145,8 @@ The Index Service maintains a cluster-wide set of index definitions and metadata
 
 The rebalance process takes into account the nodes' CPU, RAM, and disk bandwidth to limit its effect on database performance.
 
+NOTE: Shard Based Rebalance and Rebalance Based on File Transfer are synonyms for File-based Rebalance.
+
 [#index-rebalance-methods]
 ==== Index Rebalance Methods
 
@@ -228,6 +230,28 @@ This setting has no effect if you have enabled file-based index rebalancing.
 Users with Full Admin or Cluster Admin roles can change the batch size using the REST API.
 See xref:rest-api:rest-modify-index-batch-size.adoc[Modify Index Batch Size].
 
+[#smart-batching]
+==== Smart Batching
+
+During a Rebalance operation, Couchbase Server breaks the rebuilding process into batches to limit the performance impacts.
+
+The default batch size is set to 3 applying a limit on the amount of work attempted concurrently.
+
+In Couchbase Server 7.1 and later versions, you can use smart batching with one or more of the following purposes:
+
+* Reduces further time and resources required to move the index metadata.
+* Rebuilds indexes at their new locations during rebalance.
+* Increases rebalance performance by increasing pipeline parallelism by starting the next batch when the previous batch is only partially completed.
+* Allows the increase of overall concurrency by using administrator-determined modifications of the batch size.
+* Optimizes the sharing of data streams where index relocation takes place.
+* Repairs, prior to index relocation, index replicas lost due to node failure.
+* When appropriate, reassigns scheduled index-rebuilding from one batch to the next, to balance the workloads.
+
+If at least one node in the cluster is running a Server version 7.1+ then most of the smart batching features apply to the cluster where some of the nodes are running an earlier version.
+
+You can change the default batch size of 3 by the Full Admin and Cluster Admin roles using the REST API.
+For information, see xref:rest-api:rest-modify-index-batch-size.adoc[Modify Index Batch Size].
+
 [#rebalancing-the-search-service]
 === Search Service
 

modules/manage/pages/manage-settings/general-settings.adoc

@@ -313,12 +313,15 @@ During an upgrade, mixed mode clusters with nodes that support bloom filters wil
 
 [#file-based-index-rebalance]
 * *File Transfer Based Rebalance*:
-Controls whether Couchbase Server rebuilds indexes or copies them between nodes. 
+Controls whether Couchbase Server rebuilds indexes or copies them between nodes.
+Use the **Enable File Transfer Based Rebalance** checkbox to enable or disable the File Transfer Based Rebalance from the UI.
 The default cleared setting has an Index Server node rebuild any newly assigned index during a rebalance.
 You cannot enable file-based rebalance when you have enabled Memory Optimized Index Storage.  
 When you select this option, Couchbase Server copies the index files from one Index Server node to another during a rebalance instead of rebuilding them. 
 See xref:learn:clusters-and-availability/rebalance.adoc#index-rebalance-methods[Index Rebalance Methods].
 +
+NOTE: Shard Based Rebalance and Rebalance Based on File Transfer are synonyms for File-based Rebalance.
++
 You can disable this feature from the UI or via REST API. To learn about disabling this feature via REST API, see xref:rest-api:post-settings-indexes.adoc#disable-file-transfer-based-rebalance[Curl Command to Disable the File Transfer Based Rebalance]. This feature is disabled by default.
 +
 WARNING: Disabling this feature slows down the Rebalance operation.

modules/rest-api/pages/post-settings-indexes.adoc

@@ -161,6 +161,8 @@ include::example$post-settings-indexes.jsonc[]
 
 The following command disables the File Transfer Based Rebalance (`enableShardAffinity`) feature in the xref:manage:manage-settings/general-settings.adoc#index-storage-mode[Index Storage Mode].
 
+NOTE: Shard Based Rebalance and Rebalance Based on File Transfer are synonyms for File-based Rebalance.
+
 [source#example-curl,bash]
 ----
 include::example$post-settings-indexes.sh[tag=disable-ftb-rebalance]

modules/rest-api/pages/rest-modify-index-batch-size.adoc

@@ -5,6 +5,8 @@
 {description}
 
 
+NOTE: Shard Based Rebalance and Rebalance Based on File Transfer are synonyms for File-based Rebalance.
+
 == HTTP Method and URI
 
 ----