gistfile1.txt

I've been doing a bunch of auditing of the homepage (both signed in and signed out), and my latest discovery involves this unexpectedly expensive query:

select Taxonomy.taxonomy_id as Taxonomy__taxonomy_id, 
       Taxonomy.top_level_id as Taxonomy__top_level_id, 
       Taxonomy.name as Taxonomy__name, 
       Taxonomy.metadata as Taxonomy__metadata, 
       Taxonomy.shard_id as Taxonomy__shard_id, 
       Taxonomy.old_shard as Taxonomy__old_shard, 
       Taxonomy.migration_lock as Taxonomy__migration_lock, 
       Taxonomy.create_date as Taxonomy__create_date, 
       Taxonomy.update_date as Taxonomy__update_date 
from taxonomies as Taxonomy 
where Taxonomy.taxonomy_id = Taxonomy.top_level_id

This takes 20ms in prod, and runs twice on every page load it appears.  Judging from the schema, we have both taxonomy_id and top_level_id indexed, but when I run an explain I get no index used.

Apparently the indexes don't apply with column equality checks.  

I'll deal with the double query issue and make sure we only make it once, but