If you often update only some tables and can arrange your query/queries so that you don't change any indexed fields, then setting fillfactor to a lower value than the default of 100 for those tables enables PostgreSQL to use Heap-only Tuples (HOT) updates, which can be an order of magnitude faster than ordinary updates. HOT updates not only avoid creating new index entries, but can also perform a fast mini-vacuum inside the page to make room for new rows:
ALTER TABLE t1 SET (fillfactor = 70);
This tells PostgreSQL to fill only 70 percent of each page in table t1 when performing insertions so that 30 percent is left for use by in-page (HOT) updates.
