[discrete]
[[breaking_80_index_setting_changes]]
==== Index setting changes

//NOTE: The notable-breaking-changes tagged regions are re-used in the
//Installation and Upgrade Guide

//tag::notable-breaking-changes[]
[[deprecation-system-indices]]
.Direct access to system indices is deprecated.
[%collapsible]
====
*Details* +
Directly accessing system indices is deprecated, and may be prevented in a
future version. If you must access a system index, create a security role with
an index permission that targets the specific index and set the
`allow_restricted_indices` permission to `true`. Refer to 
{ref}/defining-roles.html#roles-indices-priv[indices privileges] for
information on adding this permission to an index privilege.

*Impact* +
Accessing system indices directly results in warnings in the header of API
responses. If available, use {kib} or the associated feature's {es} APIs to
manage the data that you want to access.
====

[[deprecate-max-merge-at-once-explicit-setting]]
.`index.merge.policy.max_merge_at_once_explicit` is deprecated and has no effect.
[%collapsible]
====
*Details* +
The `index.merge.policy.max_merge_at_once_explicit` index setting is deprecated
and has no effect.

Previously, you could specify `index.merge.policy.max_merge_at_once_explicit` to
set the maximum number of segments to merge at the same time during a force
merge or when expunging deleted documents. In 8.0, this number is unlimited,
regardless of the setting.

*Impact* +
Specifying `index.merge.policy.max_merge_at_once_explicit` will have no effect
but will generate deprecation warnings.

To avoid these deprecation warnings, discontinue use of the setting. Don't
specify the setting when creating new indices, and remove the setting from
index and component templates.

To remove the setting from an existing data stream or index, specify the
setting's value as `null` using the update index settings API.

[source,console]
----
PUT my-index-000001/_settings
{
  "index.merge.policy.max_merge_at_once_explicit": null
}
----
// TEST[setup:my_index]

====

[[index-max-adjacency-matrix-filters-removed]]
.The `index.max_adjacency_matrix_filters` index setting has been removed.
[%collapsible]
====
*Details* +
The `index.max_adjacency_matrix_filters` index setting has been removed.
Previously, you could use this setting to configure the maximum number of
filters for the
{ref}/search-aggregations-bucket-adjacency-matrix-aggregation.html[adjacency
matrix aggregation]. The `indices.query.bool.max_clause_count` index setting now
determines the maximum number of filters for the aggregation.

*Impact* +
Discontinue use of the `index.max_adjacency_matrix_filters` index setting.

Requests that include the index setting will return an error. If you upgrade a
cluster with a 7.x index that already contains the setting, {es} will
{ref}/archived-settings.html#archived-index-settings[archive the setting].

Remove the index setting from index and component templates. Attempts to use a
template that contains the setting will fail and return an error. This includes
automated operations, such the {ilm-init} rollover action.
====

.The `index.force_memory_term_dictionary` setting has been removed.
[%collapsible]
====
*Details* +
The `index.force_memory_term_dictionary` setting was introduced in 7.0 as a
temporary measure to allow users to opt-out of the optimization that leaves the
term dictionary on disk when appropriate. This optimization is now mandatory
and the setting is removed.

*Impact* +
Discontinue use of the `index.force_memory_term_dictionary` index setting.
Requests that include this setting will return an error.
====

.The `index.soft_deletes.enabled` setting has been removed.
[%collapsible]
====
*Details* +
Creating indices with soft deletes disabled was deprecated in 7.6 and
is no longer supported in 8.0. The `index.soft_deletes.enabled` setting
can no longer be set to `false`.

*Impact* +
Discontinue use of the `index.soft_deletes.enabled` index setting. Requests that
set `index.soft_deletes.enabled` to `false` will return an error.
====

.The `index.translog.retention.age` and `index.translog.retention.size` settings have been removed.
[%collapsible]
====
*Details* +
Translog retention settings `index.translog.retention.age` and
`index.translog.retention.size` were effectively ignored in 7.4, deprecated in
7.7, and removed in 8.0 in favor of
{ref}/index-modules-history-retention.html[soft deletes].

*Impact* +
Discontinue use of the `index.translog.retention.age` and
`index.translog.retention.size` index settings. Requests that
include these settings will return an error.
====
//end::notable-breaking-changes[]