On Thu, Dec 6, 2012 at 3:58 AM, Vlad Arkhipov <arhi...@dc.baikal.ru> wrote: > In a BEFORE UPDATE trigger I need to know whether the row was previously > modified by this transaction. Is it safe to use xmin and txid_current() for > this purpose (xmin is 32-bit txid type but txid_current() returns 64-bit > bigint). > > CREATE FUNCTION test_trigger() > RETURNS TRIGGER AS $$ > BEGIN > IF OLD.xmin = txid_current() THEN > -- Do something. > ELSE > -- Do something else. > END IF; > END; > $$ LANGUAGE plpgsql;
txid_current() will return a different value from xmin after the XID space has wrapped around at least once; also, you might need to consider subtransactions. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
