--- title: ALTER INDEX description: The ALTER INDEX statement increases or decreases the number of index replicas and partition replicas. pubDate: 2026-08-17T09:53:44.266Z antora: editUrl: https://github.com/couchbaselabs/docs-devex/edit/capella/modules/n1ql/pages/n1ql-language-reference/alterindex.adoc xref: xref:cloud:n1ql:n1ql-language-reference/alterindex.adoc[] --- [Consult the llms.txt file for a full list of contents](/llms.txt) [View original HTML](/cloud/n1ql/n1ql-language-reference/alterindex.html) # ALTER INDEX > The ALTER INDEX statement increases or decreases the number of index replicas and partition replicas. The [ALTER VECTOR INDEX](altervectorindex.md) statement is a synonym for the ALTER INDEX statement. Both statements have the same functionality. ## [](#purpose)Purpose You can use the `ALTER INDEX` statement to increase or decrease the number of replicas, or to drop a specified index replica temporarily. You can also use it to perform the same alterations to a partitioned index and any replica partitions. You may use this statement when you encounter any of the following situations: * An imbalance occurs due to a particular index growing faster than expected, and a replica is needed on a different node. * An imbalance occurs due to a cluster of indexes being dropped on a single node. * A node is scheduled for removal, and its index replicas need to be dropped. * The automated process of rebalancing does not give the expected results. * Other types of scaling up or scaling down are needed. If a node goes down while an ALTER INDEX operation is happening, then the index would rollback to its original node (not affecting queries) and a notification would appear. ## [](#prerequisites)Prerequisites To execute this statement, your client must have necessary privileges on the keyspace that contains the index. The required privilege depends on your [cluster access credential type](../../clusters/cluster-rbac.md#cluster-access-credential-types). | Credential Type | Privilege | | --------------- | ---------------------------------------------------------------------------------------- | | Basic | [Write](../../clusters/cluster-rbac.md#basic-access-credentials) | | Advanced | [Query Index](../../clusters/cluster-rbac.md#privileges-for-advanced-access-credentials) | ## [](#syntax)Syntax ```ebnf alter-index ::= 'ALTER' 'INDEX' ( index-path '.' index-name | index-name 'ON' keyspace-ref ) index-using? index-with ``` ![Syntax diagram: see source code listing](../_images/n1ql-language-reference/alter-index.png) The ALTER INDEX statement provides 2 possible syntaxes for specifying the index and the keyspace where the index is located. | index-name | (Required) A unique name that identifies the index. | | ------------ | ------------------------------------------------------------------------------------------------------------------------ | | index-path | (Optional) One possible syntax for specifying the keyspace. See [Index Path](#index-path). | | keyspace-ref | (Optional) The other possible syntax for specifying the keyspace. See [Index Name ON Keyspace Reference](#keyspace-ref). | | index-using | (Optional) Specifies the index type. See [USING Clause](#index-using). | | index-with | (Required) Specifies options for the index. See [WITH Clause](#index-with). | ### [](#index-path)Index Path ```ebnf index-path ::= keyspace-full | keyspace-prefix | keyspace-partial ``` ![Syntax diagram: see source code listing](../_images/n1ql-language-reference/index-path.png) You can use a dotted notation to specify the index and the keyspace on which the index is built. This syntax provides compatibility with legacy versions of Couchbase Server. The index path may be a [full keyspace path](#keyspace-full-index), a [keyspace prefix](#keyspace-prefix-index), or a [keyspace partial](#keyspace-partial-index). > [!NOTE] > If there is a hyphen (-) inside the index name or any part of the index path, you must wrap the index name or that part of the index path in backticks (\` \`). See the examples on this page. #### [](#keyspace-full-index)Index Path: Full Keyspace ```ebnf keyspace-full ::= namespace ':' bucket '.' scope '.' collection ``` ![Syntax diagram: see source code listing](../_images/n1ql-language-reference/keyspace-full.png) If the index is built on a named collection, the index path may be a full keyspace path, including namespace, bucket, scope, and collection, followed by the index name. In this case, the [query context](../n1ql-intro/queriesandresults.md#query-context) is ignored. | namespace | (Required) An [identifier](identifiers.md) that refers to the [namespace](../n1ql-intro/queriesandresults.md#logical-hierarchy) of the keyspace. Currently, only the default namespace is available. | | ---------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | bucket | (Required) An [identifier](identifiers.md) that refers to the [bucket name](../n1ql-intro/queriesandresults.md#logical-hierarchy) of the keyspace. | | scope | (Required) An [identifier](identifiers.md) that refers to the [scope name](../n1ql-intro/queriesandresults.md#logical-hierarchy) of the keyspace. | | collection | (Required) An [identifier](identifiers.md) that refers to the [collection name](../n1ql-intro/queriesandresults.md#logical-hierarchy) of the keyspace. | For example, `` default:`travel-sample`.inventory.airline.`idx-name` `` indicates the `idx-name` index on the `airline` collection in the `inventory` scope in the `` default:`travel-sample` `` bucket. #### [](#keyspace-prefix-index)Index Path: Keyspace Prefix ```ebnf keyspace-prefix ::= ( namespace ':' )? bucket ``` ![Syntax diagram: see source code listing](../_images/n1ql-language-reference/keyspace-prefix.png) If the index is built on the default collection in the default scope within a bucket, the index path may be just an optional namespace and the bucket name, followed by the index name. In this case, the [query context](../n1ql-intro/queriesandresults.md#query-context) should not be set. | namespace | (Optional) An [identifier](identifiers.md) that refers to the [namespace](../n1ql-intro/queriesandresults.md#logical-hierarchy) of the keyspace. Currently, only the default namespace is available. If the namespace name is omitted, the default namespace in the current session is used. | | --------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | bucket | (Required) An [identifier](identifiers.md) that refers to the [bucket name](../n1ql-intro/queriesandresults.md#logical-hierarchy) of the keyspace. | For example, `` default:`travel-sample`.def_type `` indicates the `def_type` index on the default collection in the default scope in the `` default:`travel-sample` `` bucket. #### [](#keyspace-partial-index)Index Path: Keyspace Partial ```ebnf keyspace-partial ::= collection ``` ![Syntax diagram: see source code listing](../_images/n1ql-language-reference/keyspace-partial.png) Alternatively, if the keyspace is a named collection, the index path may be just the collection name, followed by the index name. In this case, you must set the [query context](../n1ql-intro/queriesandresults.md#query-context) to indicate the required namespace, bucket, and scope. | collection | (Required) An [identifier](identifiers.md) that refers to the [collection name](../n1ql-intro/queriesandresults.md#logical-hierarchy) of the keyspace. | | ---------- | ------------------------------------------------------------------------------------------------------------------------------------------------------ | For example, `` airline.`idx-name` `` indicates the `idx-name` index on the `airline` collection, assuming that the query context is set. ### [](#keyspace-ref)Index Name ON Keyspace Reference ```ebnf keyspace-ref ::= keyspace-path | keyspace-partial ``` ![Syntax diagram: see source code listing](../_images/n1ql-language-reference/keyspace-ref.png) You can use the index name with the `ON` keyword and a keyspace reference to specify the keyspace on which the index is built. The keyspace reference may be a [keyspace path](#keyspace-path) or a [keyspace partial](#keyspace-partial). > [!NOTE] > If there is a hyphen (-) inside the index name or any part of the keyspace reference, you must wrap the index name or that part of the keyspace reference in backticks (\` \`). See the examples on this page. #### [](#keyspace-path)Keyspace Reference: Keyspace Path ```ebnf keyspace-path ::= ( namespace ':' )? bucket ( '.' scope '.' collection )? ``` ![Syntax diagram: see source code listing](../_images/n1ql-language-reference/keyspace-path.png) If the keyspace is a named collection, or the default collection in the default scope within a bucket, the keyspace reference may be a keyspace path. In this case, the [query context](../n1ql-intro/queriesandresults.md#query-context) should not be set. | namespace | (Optional) An [identifier](identifiers.md) that refers to the [namespace](../n1ql-intro/queriesandresults.md#logical-hierarchy) of the keyspace. Currently, only the default namespace is available. If the namespace name is omitted, the default namespace in the current session is used. | | ---------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | bucket | (Required) An [identifier](identifiers.md) that refers to the [bucket name](../n1ql-intro/queriesandresults.md#logical-hierarchy) of the keyspace. | | scope | (Optional) An [identifier](identifiers.md) that refers to the [scope name](../n1ql-intro/queriesandresults.md#logical-hierarchy) of the keyspace. If omitted, the bucket's default scope is used. | | collection | (Optional) An [identifier](identifiers.md) that refers to the [collection name](../n1ql-intro/queriesandresults.md#logical-hierarchy) of the keyspace. If omitted, the default collection in the bucket's default scope is used. | For example, `` def_type ON default:`travel-sample` `` indicates the `def_type` index on the default collection in the default scope in the `` default:`travel-sample` `` bucket. Similarly, `` `idx-name` ON default:`travel-sample`.inventory.airline `` indicates the `idx-name` index on the `airline` collection in the `inventory` scope in the `` default:`travel-sample` `` bucket. #### [](#keyspace-partial)Keyspace Reference: Keyspace Partial ```ebnf keyspace-partial ::= collection ``` ![Syntax diagram: see source code listing](../_images/n1ql-language-reference/keyspace-partial.png) Alternatively, if the keyspace is a named collection, the keyspace reference may be just the collection name. In this case, you must set the [query context](../n1ql-intro/queriesandresults.md#query-context) to indicate the required namespace, bucket, and scope. | collection | (Required) An [identifier](identifiers.md) that refers to the [collection name](../n1ql-intro/queriesandresults.md#logical-hierarchy) of the keyspace. | | ---------- | ------------------------------------------------------------------------------------------------------------------------------------------------------ | For example, `` `idx-name` ON airline `` indicates the `idx-name` index on the `airline` collection, assuming the query context is set. ### [](#index-using)USING Clause ```ebnf index-using ::= 'USING' 'GSI' ``` ![Syntax diagram: see source code listing](../_images/n1ql-language-reference/index-using.png) The index type for a secondary index must be Global Secondary Index (GSI). The `USING GSI` keywords are optional and may be omitted. ### [](#index-with)WITH Clause ```ebnf index-with ::= 'WITH' expr ``` ![Syntax diagram: see source code listing](../_images/n1ql-language-reference/index-with.png) Use the `WITH` clause to specify additional options. | expr | An object with the following properties. | | ---- | ---------------------------------------- | | Name | Description | Schema | | --------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------ | | **action** _required_ | A string denoting the operation to be performed. The possible values are: move You cannot use this action in Couchbase Capella, as it defaults to file-based index rebalancing. replica\_count Alters the number of replicas. You must use the num\_replica property to specify the required number of replicas. The planner decides where to place any new index replicas on the available index nodes, based on the server load. In Couchbase Capella, you cannot restrict the placement of index replicas to specified nodes. drop\_replica Drops a specified replica temporarily; for example, to repair a replica. You must use the replicaId property to specify the replica to drop. | enum (move, replica\_count, drop\_replica) | | **num\_replica** _optional_ | Required if action is set to replica\_count. An integer specifying the number of replicas of the index. The index service will automatically distribute these indexes amongst the index nodes in the cluster for load balancing and high availability purposes. The index service attempts to distribute the replicas based on the server groups in use in the cluster where possible. (In Couchbase Capella, you cannot restrict the placement of index replicas to specified nodes.) | Integer | | **nodes** _optional_ | You cannot use this property in Couchbase Capella, as it defaults to file-based index rebalancing. | String array | | **replicaId** _optional_ | Required if action is set to drop\_replica. An integer, specifying a replica ID. | Integer | ## [](#usage)Usage If you attempt to alter an index which is still scheduled for background creation, the request fails. The statement will not work while the cluster is undergoing a rebalance. ### [](#moving-an-index-or-index-replicas)Moving an Index or Index Replicas You cannot use this statement to move indexes or index replicas in Couchbase Capella, as it defaults to file-based index rebalancing. Likewise, you cannot use this statement to repartition an index across a different number of nodes. ### [](#changing-the-replica-count)Changing the Replica Count When changing the number of replicas, the specified number of replicas must be less than the number of index nodes available for placement. If the specified number of replicas is greater than or equal to the number of index nodes available for placement, then the operation will fail. In Couchbase Capella, you cannot restrict the placement of index replicas to specified nodes. When increasing the number of replicas, no single index node will host more than 1 replica of the same index, or the same partition of the same index. Replicas are distributed across the available server groups. When reducing the number of replicas, the index service will first drop unhealthy replicas, where an unhealthy replica is a replica with missing partitions. After all unhealthy replicas are dropped, the index service will if necessary drop replicas with the highest replica ID. An unhealthy replica may not have the highest replica ID, so after an index reduction there may be gaps in the sequence of replica IDs — for example, 1, 2, 4, where replica ID 3 was dropped. ### [](#dropping-a-specific-replica)Dropping a Specific Replica When dropping a replica, the index topology does not change. The indexing service remembers the number of partitions and replicas specified for this index. Given sufficient capacity, the dropped replica is rebuilt after the next rebalance — although it may be placed on a different index node, depending on the resource usage statistics of the available nodes. To find the ID of an index replica and see which node it's placed on, you can use the [Indexes page in the Couchbase Capella UI](../../clusters/index-service/manage-indexes.md) or query the [system:indexes](../n1ql-intro/sysinfo.md#querying-indexes) catalog. When dropping a replica, it's possible to leave a server group with no replica. For a partitioned index, run a rebalance to move a replica into the vacant server group. ### [](#index-redistribution)Index Redistribution Couchbase Capella redistributes indexes automatically on rebalance. For more information, see [Rebalance](../../clusters/scale-database.md#rebalance). ## [](#return-value)Return Value If the statement succeeds, then: * The query returns an empty array. * The index alteration is visible in the Indexes tab. * After the alteration is complete, the new indexes begin to service query scans. If the statement fails, then: * The original indexes continue to service query scans. * The UI Log and Query tab have the appropriate error message. * Some common errors include: | Error Message | Possible Cause | | ----------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------- | | GSI index xxxxxxxx not found | Mistyped an index name | | move index is disabled | Attempted to move a replica | | "nodes" clause is disabled with alter index as file based rebalance (shard affinity) is enabled | Attempted to restrict replicas to specified nodes when altering the number of replicas | | syntax error - at \\",\\" | Missed a double-quote mark (") | | Fail to alter index: Fail to drop replica | Replica does not exist or was mistyped | | Unsupported action value | Mistyped the "action" | ## [](#examples)Examples To try the examples in this section, set the query context to the `inventory` scope in the travel sample dataset. For more information, see [Query Context](../n1ql-intro/queriesandresults.md#query-context). The examples in this section assume that you have a cluster with at least 4 nodes. The nodes are named `svc-dqi-node-001`, `svc-dqi-node-002`, and `svc-dqi-node-003`, and `svc-dqi-node-004`. The nodes in your cluster may have different names or IP addresses. Example 1\. Increasing the number of replicas Create an index on node `svc-dqi-node-001` with replicas on nodes `svc-dqi-node-002` and `svc-dqi-node-003`, then increase the number of replicas to 4\. New replicas may be placed on any available index nodes in the cluster. ```sqlpp CREATE INDEX country_idx ON airport(country, city) WITH {"nodes": ["svc-dqi-node-001:18091", "svc-dqi-node-002:18091", "svc-dqi-node-003:18091"]}; ALTER INDEX country_idx ON airport WITH {"action": "replica_count", "num_replica": 4}; ``` Example 2\. Decreasing the number of replicas Create an index on node `svc-dqi-node-001` with replicas on nodes `svc-dqi-node-002` and `svc-dqi-node-003`, then decrease the number of replicas to 1. ```sqlpp CREATE INDEX country_idx ON airport(country, city) WITH {"nodes": ["svc-dqi-node-001:18091", "svc-dqi-node-002:18091", "svc-dqi-node-003:18091"]}; ALTER INDEX country_idx ON airport WITH {"action": "replica_count", "num_replica": 1}; ``` Example 3\. Dropping a specific replica Create an index with 2 replicas, and specify that nodes `svc-dqi-node-001`, `svc-dqi-node-002`, `svc-dqi-node-003`, and `svc-dqi-node-004` should be available for index and replica placement. Then delete replica 2. ```sqlpp CREATE INDEX country_idx ON airport(country, city) USING GSI WITH {"num_replica": 2, "nodes": ["svc-dqi-node-001:18091", "svc-dqi-node-002:18091", "svc-dqi-node-003:18091", "svc-dqi-node-004:18091"]}; ALTER INDEX country_idx ON airport WITH {"action": "drop_replica", "replicaId": 2}; ``` ## [](#related-links)Related Links * [Primary and Secondary Index Reference](../../indexes/indexing-overview.md) * [Filtered Search Using Composite Vector Indexes](../../vector-index/composite-vector-index.md) * [Vector Search Using Hyperscale Vector Indexes](../../vector-index/hyperscale-vector-index.md) * [CREATE PRIMARY INDEX](createprimaryindex.md)| [CREATE INDEX](createindex.md)| [CREATE VECTOR INDEX](createvectorindex.md) * [BUILD INDEX](build-index.md) * [ALTER VECTOR INDEX](altervectorindex.md) * [DROP PRIMARY INDEX](dropprimaryindex.md)| [DROP INDEX](dropindex.md)| [DROP VECTOR INDEX](dropvectorindex.md)