Loading a config with a large tag node, such as a prefix-list with many rules, takes time proportional to the square of its size: at boot and on load. A 10,000-rule list made the boot-time config load take 50 minutes.

Root cause.

• Cstore::add_tag (src/cstore/cstore.cpp) lists every existing value of the tag node, through the session's unionfs-fuse mount, each time it adds a value.
• The list is used only to enforce a tag limit, and that limit is 0 (off) for almost every node.
• Adding n values therefore reads about n²/2 directory entries.

Measurements

Fix direction. Call get_all_child_node_names only when tlimit > 0, the only case that uses the result. Behaviour is unchanged for nodes with and without a limit.