Hi, On 2019-05-09 13:03:50 -0700, Erik Jones wrote: > The question then is: Why would these user queries be waiting on an > AccessShare lock on pg_attribute? Thus far we've been unable to recreate > any transacitons with the above query (and others) that show any > pg_attribute locks. There is no ORM in play here and these queries are > being sent as single query transactions via this Node.js postgres adapter: > https://github.com/brianc/node-postgres which is pretty bare bones. Queries that access a table for the *first* time after DDL happened (including truncating the relation), need an AccessShareLock on pg_attribute (and pg_class, pg_index, ...) for a short time. You can reproduce that fairly easily: S1: CREATE TABLE foo(); S2: BEGIN; LOCK pg_attribute; S1: SELECT * FROM foo; S2: COMMIT; S1 could execute the select, because it has a cached view of the way the relation looks. S2: ALTER TABLE foo ADD COLUMN bar INT; S2: BEGIN; LOCK pg_attribute; S1: SELECT * FROM foo; Here S1 is blocked, because it needs to look at pg_attribute to figure out the "shape" of the table, but it's currently locked. Greetings, Andres Freund
