[[index-modules-blocks]]
== Index blocks

Index blocks limit the kind of operations that are available on a certain
index. The blocks come in different flavours, allowing to block write,
read, or metadata operations. The blocks can be set / removed using dynamic
index settings, or can be added using a dedicated API, which also ensures
for write blocks that, once successfully returning to the user, all shards
of the index are properly accounting for the block, for example that all
in-flight writes to an index have been completed after adding the write
block.

[discrete]
[[index-block-settings]]
=== Index block settings

The following _dynamic_ index settings determine the blocks present on an
index:

`index.blocks.read_only`::

    Set to `true` to make the index and index metadata read only, `false` to
    allow writes and metadata changes.

`index.blocks.read_only_allow_delete`::

    Similar to `index.blocks.read_only`, but also allows deleting the index to
    make more resources available. The <<disk-based-shard-allocation,disk-based shard
    allocator>> may add and remove this block automatically.
+
Deleting documents from an index to release resources - rather than deleting the index itself - can increase the index size over time. When `index.blocks.read_only_allow_delete` is set to `true`, deleting documents is not permitted. However, deleting the index itself releases the read-only index block and makes resources available almost immediately.
+
IMPORTANT: {es} adds and removes the read-only index block automatically when the disk utilization falls below the high watermark, controlled by <<cluster-routing-flood-stage,cluster.routing.allocation.disk.watermark.flood_stage>>.

`index.blocks.read`::

    Set to `true` to disable read operations against the index.

`index.blocks.write`::

    Set to `true` to disable data write operations against the index. Unlike `read_only`,
    this setting does not affect metadata. For instance, you can close an index with a `write`
    block, but you cannot close an index with a `read_only` block.

`index.blocks.metadata`::

    Set to `true` to disable index metadata reads and writes.

`index.blocks.read_only_allow_delete`::

    Similar to `index.blocks.read_only`, but also allows deleting the index to
    make more resources available. The <<disk-based-shard-allocation,disk-based shard
    allocator>> adds and removes this block automatically.

Deleting documents from an index - rather than deleting the index itself - can
in fact increase the index size. When you are running out of disk space
`index.blocks.read_only_allow_delete` is set to `true`, preventing you from
consuming more disk space by deleting some documents. However, this block does
permit you to delete the index itself since this does not require any extra
disk space. When you delete an index the data is removed from disk almost
immediately, freeing the space it consumes.

IMPORTANT: {es} adds the read-only-allow-delete index block automatically when
disk utilisation exceeds the <<cluster-routing-flood-stage,flood-stage
watermark>> and removes it again when disk utilisation is below the
<<cluster-routing-watermark-high,high watermark>>. You should not apply this
block yourself.

[discrete]
[[add-index-block]]
=== Add index block API

Adds an index block to an index.

[source,console]
--------------------------------------------------
PUT /twitter/_block/write
--------------------------------------------------
// TEST[setup:twitter]


[discrete]
[[add-index-block-api-request]]
==== {api-request-title}

`PUT /<index>/_block/<block>`


[discrete]
[role="child_attributes"]
[[add-index-block-api-path-params]]
==== {api-path-parms-title}

include::{es-repo-dir}/rest-api/common-parms.asciidoc[tag=index]
+
To add blocks to all indices, use `_all` or `*`. To disallow the adding
of blocks to indices with `_all` or wildcard expressions,
change the `action.destructive_requires_name` cluster setting to `true`.
You can update this setting in the `elasticsearch.yml` file
or using the <<cluster-update-settings,cluster update settings>> API.
`<block>`::
(Required, string)
Block type to add to the index.
+
.Valid values for `<block>`
[%collapsible%open]
====
`metadata`::
Disable metadata changes, such as closing the index.

`read`::
Disable read operations.

`read_only`::
Disable write operations and metadata changes.

`write`::
Disable write operations. However, metadata changes are still allowed.
====
[discrete]
[[add-index-block-api-query-params]]
==== {api-query-parms-title}

include::{es-repo-dir}/rest-api/common-parms.asciidoc[tag=allow-no-indices]
+
Defaults to `true`.

include::{es-repo-dir}/rest-api/common-parms.asciidoc[tag=expand-wildcards]
+
Defaults to `open`.

include::{es-repo-dir}/rest-api/common-parms.asciidoc[tag=index-ignore-unavailable]

include::{es-repo-dir}/rest-api/common-parms.asciidoc[tag=timeoutparms]

[discrete]
[[add-index-block-api-example]]
==== {api-examples-title}

The following example shows how to add an index block:

[source,console]
--------------------------------------------------
PUT /my_index/_block/write
--------------------------------------------------
// TEST[s/^/PUT my_index\n/]

The API returns following response:

[source,console-result]
--------------------------------------------------
{
    "acknowledged" : true,
    "shards_acknowledged" : true,
    "indices" : [ {
        "name" : "my_index",
        "blocked" : true
    } ]
}
--------------------------------------------------