gwc tile layer load performance regression at startup

Description

DefaultTileLayerCatalog listens to Resouce events under
the data directory's gwc-layers folder resource in order to
notify its local instance listeners of tile layer configuration
changes even when on a shared directory by several service
instances.

To do so, it uses both a "folder" listener on gwc-layers,
and one listener per tile layer info resource (i.e. gwc-layers/*.xml).

This results in a severe startup hit when there are several
tile layers.

A pull request has already been applied on master (https://github.com/geoserver/geoserver/pull/3451) and needs to be backported to 2.15.x. 2.14.x is not affected.

Environment

None

Status

Assignee

Gabriel Roldan

Reporter

Gabriel Roldan

Triage

None

Fix versions

Affects versions

2.15.1

Components

Priority

Medium
Configure