[discrete]
[[breaking_80_jvm_option_changes]]
==== JVM option changes

TIP: {ess-skip-section}

[[breaking_80_allocation_change_flood_stage_block_always_removed]]
.`es.disk.auto_release_flood_stage_block` has been removed.
[%collapsible]
====
*Details* +
If a node exceeds the flood-stage disk watermark then we add a block to all of
its indices to prevent further writes as a last-ditch attempt to prevent the
node completely exhausting its disk space. By default, from 7.4 onwards the
block is automatically removed when a node drops below the high watermark
again, but this behaviour could be disabled by setting the system property
`es.disk.auto_release_flood_stage_block` to `false`. This behaviour is no
longer optional, and this system property must now not be set.

*Impact* +
Discontinue use of the `es.disk.auto_release_flood_stage_block` system property.
Setting this system property will result in an error on startup.
====

.`es.rest.url_plus_as_space` has been removed.
[%collapsible]
====
*Details* +
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.
In these previous versions, if your application required handling `+` as a single space, you could 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.

*Impact* +
Update your application or workflow to assume `+` in a URL is encoded as `%2B`.
====

.`es.unsafely_permit_handshake_from_incompatible_builds` has been removed.
[%collapsible]
====
*Details* +
{es} has a check that verifies that communicating pairs of nodes of the same
version are running exactly the same build and therefore using the same wire
format as each other. In previous versions this check can be bypassed by
setting the system property
`es.unsafely_permit_handshake_from_incompatible_builds` to `true`. The use of
this system property is now forbidden.

*Impact* +
Discontinue use of the `es.unsafely_permit_handshake_from_incompatible_builds`
system property, and ensure that all nodes of the same version are running
exactly the same build. Setting this system property will result in an error
on startup.
====