Re: Query doesn't use index on hstore column

Well, first off, a btree index is fairly useless for this query,
because btree has no concept that the hstore has any sub-structure.
A GIN index or GIST index could work though.  Secondly, you have to
remember that indexable WHERE conditions in Postgres are *always* of
the form "WHERE indexed_column indexable_operator some_comparison_value".

You might care to read
http://www.postgresql.org/docs/9.4/static/indexes.html
to get a better handle on what Postgres indexes can and can't do.