Kendra Little does a bit of index management:
Dear Postgres, Why won’t you use my covering index?
Lately I’ve been learning to tune queries running against PostgreSQL, and it’s pretty delightful. One fun question that I worked through struck me something that most Postgres users probably encounter one way or another: sometimes you may create the perfect index that covers a given query, but the query planner will choose to ignore it and scan the base table.
Why in the world would it do that?
Read on to learn why.