For some pages up to 29% of the rendering time is spent in AbstractResource.getChild. In my case, 75% of the resources are MergedResources and the rest are JcrNodeResources (for which I have already opened
Therefore, I would suggest implementing the following optimization:
The merged resources should be stored in MergedResource and when getChild is called, it would use getChild on them directly and merge the child resources. This would have the advantage that the ParentHidingHandler would not have to be called again for the parent resources and could even make
SLING-4568 obsolete. Moreover, it would leverage optimizations of the merged resource implementations (e.g. SLING-4596 for JcrNodeResource#getChild).
A problem with this approach is that possible in JCR (and maybe also some other resource providers) to set ACLs which allow to read children but not their parents. Therefore, getChild will in addition have to check for each search path which isn't covered with a merged resource if this path does really not exist.