Following change I189ba71de, the hierarchical list in
Special:Allpages becomes a simple alphabetic pager if the total number
of pages exceeds a safety threshold. The threshold is designed to
protect wikis on which the load generated by the process of generating
the hierarchical list would be prohibitively expensive (bug 56840).
I189ba71de resolved the immediate operational issue, but there is a
further question of whether we want to keep the hierarchical list at
all, especially given that it cannot be enabled (in its current
implementation, at least) on larger installations.
From my perspective, the ideal outcome of this
discussion would be
that we agree that the hierarchical list is a poor fit for the
MediaWiki of today, and we resolve to remove it from core.
According to stats.grok.se, enwiki's Special:Allpages receives
approximately 158 hits a day.