The PostgreSQL GUC track_activity_query_size specifies the number of bytes reserved to track the currently executing command for each active session for pg_stat_activity, with a default of 1024.
Queries in most Mapnik stylesheets exceed this, including Meddo. Vector tile queries tend to involve lots of UNION ALL statements.
I recommend increasing it to 16384, so if we have a slow query or stuck query we can see what it is to EXPLAIN it or debug it locally. The longest current query is 4936 bytes before Mapnik inserts additional text.
This would cost 15kb more memory per connection slot, an insignificant amount.