On 2018-Jul-20, Praveen Kumar wrote:
> Regarding UPDATEs on rows that are locked via "SELECT FOR UPDATE" in > another transaction, I read the above as follows: other transactions that > attempt UPDATE of these rows will be blocked until the current transaction > ( which did "SELECT FOR UPDATE" for those rows ) ends, unless the columns > in these rows being UPDATE'ed are those that don't have a unique index on > them that can be used in a foreign key. > > Is this correct ? No. What it means that if you UPDATE the columns-indexed-by-unique-idx then the FOR UPDATE lock is acquired underneath. If your UPDATE modifies some other column, then a FOR NO KEY UPDATE lock is acquired instead. In both cases, concurrent transactions would be blocked rather than erroring out. -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
