Add index on topo.relation(topogeo_id, layer_id) ?

[strk]

Operations like getting elements of a TopoGeometry (for TopoGeom::geometry cast) or clearing a TopoGeometry would benefit from such index.

It could be a set of partial indices (per layer) or a single index, not sure what would perform better. I'm not even sure we want this to be done by core, but it seems clear to me that such an index would speed up operations at the TopoGeometry level

[strk]

Related ticket: #2083

[strk]

Upon adding such index, we'd need a function to warn user when such index is missing (TopologySummary?) and a function to add the index if missing. When adding a missing index we should maybe consider eventual indices added by users, which may either conflict in name or be useless duplicate after adding our own.

[strk]

The existing relation_layer_id_topogeo_id_element_id_element_type_key index is already effective in looking for components of topogeometries, closing this as done/not-needed