Menu performance fix - only render required links

[Ian Booth]

When rendering pages/views, there are performance issues in the way menus are handled. Two relevant examples:

1. Many templates define an instance of a menu at the start of the markup to avoid the cost of duplicate instances, but we know that the menu will be reinstantiated in a portlet. Creating reusable markup often means death by menu queries

2. canonical.launchpad.webapp.MenuBase class eagerly iterates over all menu links during setup (and hence executes all required underlying database queries to construct the link) even if the links are not actually rendered.

A performance oops illustrating a concrete impact of this problem:

OOPS-1737M2079 Person:+subscribedbranches

One fix is to modify menu infrastructure so that only the menu links are only instantiated as required by the page template. This solves the major performance issue and means the impact of creating the same menu instances more than once are eliminated for all practical purposes.

[Launchpad QA Bot (lpqabot)]

Fixed in stable r11838 <http://bazaar.launchpad.net/~launchpad-pqm/launchpad/stable/revision/11838>.