... and they're great! Postgres is very smart about using them, too, so they can be a lifesaver when you have a large table of which you only [typically] use a small bit.
I've created partial indexes over geospatial data. There are 1M doctors in the US, so answering the question "how many doctors are in San Francisco" requires a join between indexes of all doctors in the US and all businesses in SF. Using partial indexes, we carved up the country into a bunch of polygons and were able to frame the question as "how many doctors are in San Francisco in polygon 34?". Much faster.
... and they're great! Postgres is very smart about using them, too, so they can be a lifesaver when you have a large table of which you only [typically] use a small bit.
I've created partial indexes over geospatial data. There are 1M doctors in the US, so answering the question "how many doctors are in San Francisco" requires a join between indexes of all doctors in the US and all businesses in SF. Using partial indexes, we carved up the country into a bunch of polygons and were able to frame the question as "how many doctors are in San Francisco in polygon 34?". Much faster.