Comment by zacksiri
3 years ago
Yes, one of the theory was that the index wasn't the problem because there was already a multi column index on that particular column. However the PG analyze tool showed some particular query didn't utilize the index, so there needed to be a separate index just for that particular column.
The number of reasons why an RDBMS - especially Postgres - can choose to not use an index is wide. Sometimes it’s your fault, sometimes it’s the table statistics fault.
Good on you for actually empirically determining reality.