[[breaking-changes-7.4]]
== Breaking changes in 7.4
++++
<titleabbrev>7.4</titleabbrev>
++++

This section discusses the changes that you need to be aware of when migrating
your application to Elasticsearch 7.4.

See also <<release-highlights>> and <<es-release-notes>>.

coming[7.4.0]

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

//tag::notable-breaking-changes[]

// end::notable-breaking-changes[]

[[breaking_74_plugin_changes]]
=== Plugins changes

[float]
==== TokenizerFactory changes

TokenizerFactory now has a `name()` method that must be implemented.  Most
plugin-provided TokenizerFactory implementations will extend `AbstractTokenizerFactory`,
which now takes a `name` parameter in its constructor.

[float]
[[breaking_74_search_changes]]
=== Search Changes

[float]
==== Forbid empty doc values in vector functions
If a document doesn't have a value for a vector field (dense_vector
or sparse_vector) on which a vector function is executed, an error will
be thrown.

[float]
[[breaking_74_snapshots_changes]]
=== Snapshot and Restore changes

[float]
==== The S3 repository plugin uses the DNS style access pattern by default

Starting in version 7.4 the `repository-s3` plugin does not use the
now-deprecated path-style access pattern by default. In versions 7.0, 7.1, 7.2
and 7.3 the `repository-s3` plugin always used the path-style access pattern.
This is a breaking change for deployments that only support path-style access
but which are recognized as supporting DNS-style access by the AWS SDK. If your
deployment only supports path-style access and is affected by this change then
you must configure the S3 client setting `path_style_access` to `true`. This
breaking change was made necessary by
https://aws.amazon.com/blogs/aws/amazon-s3-path-deprecation-plan-the-rest-of-the-story/[AWS's
announcement] that the path-style access pattern is deprecated and will be
unsupported on buckets created after September 30th 2020.

[float]
[[breaking_80_http_changes]]
=== HTTP changes

[float]
==== Changes to Encoding Plus Signs in URLs

Starting in version 7.4, a `+` in a URL will be encoded as `%2B` by all REST API functionality. Prior versions handled a `+` as a single space.
If your application requires handling `+` as a single space you can return to the old behaviour by setting the system property
`es.rest.url_plus_as_space` to `true`. Note that this behaviour is deprecated and setting this system property to `true` will cease
to be supported in version 8.

[float]
[[breaking_74_cluster_changes]]
=== Cluster changes

[float]
==== Rerouting after starting a shard runs at lower priority

After starting each shard the elected master node must perform a reroute to
search for other shards that could be allocated. In particular, when creating
an index it is this task that allocates the replicas once the primaries have
started. In versions prior to 7.4 this task runs at priority `URGENT`, but
starting in version 7.4 its priority is reduced to `NORMAL`. In a
well-configured cluster this reduces the amount of work the master must do, but
means that a cluster with a master that is overloaded with other tasks at
`HIGH` or `URGENT` priority may take longer to allocate all replicas.

Additionally, before 7.4 the `GET
_cluster_health?wait_for_no_initializing_shards` and `GET
_cluster/health?wait_for_no_relocating_shards` APIs would return only once all
pending reroutes have completed too, but starting in version 7.4 if you want to
wait for the rerouting process to completely finish you should add the
`wait_for_events=languid` query parameter when calling these APIs.

[float]
[[breaking_74_allocation_changes]]
=== Allocation changes

[float]
==== Auto-release of read-only-allow-delete block

If a node exceeds the flood-stage disk watermark then {es} adds the
`index.blocks.read_only_allow_delete` block to all of its indices to prevent
further writes, as a last-resort attempt to prevent the node completely
exhausting its disk space. In earlier versions this block would remain in place
until manually removed, causing confusion for users who currently have ample
disk space and who are not aware that they nearly ran out at some point in the
past. From 7.4 onwards the block is automatically removed when the node drops
below the high watermark again, with the expectation that the high watermark is
some distance below the flood-stage watermark and therefore the disk space
problem is truly resolved. Since this block may be automatically removed, you
can no longer rely on adding this block manually to prevent writes to an index.
You should use the `index.blocks.read_only` block instead. This behaviour can
be disabled by setting the system property
`es.disk.auto_release_flood_stage_block` to `false`.
