On Mon, Jun 19, 2017 at 4:51 PM, Peter Geoghegan <pg@xxxxxxx> wrote: > This would make only the first lookup for each distinct value on the > outer side actually do an index scan on the inner side. I can imagine > the optimization saving certain queries from consuming a lot of memory > bandwidth, as well as saving them from pinning and locking the same > buffers repeatedly. Apparently this is sometimes called block nested loop join, and MySQL has had it for a while now: https://en.wikipedia.org/wiki/Block_nested_loop It doesn't necessarily require that the outer side input be sorted, because you might end up using a hash table, etc. -- Peter Geoghegan -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
