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

Components

Priority

Medium
Configure