Note that these errors most of the time only happens very briefly at the same time as the ALTER is run. When I did some experiments today the server in total had around 3k req/s with maybe 0.1% of them touching the table being updated, and the error then happens maybe 1-10% of the times I try this operation. If I do the operation on a table with more load the error will happen more frequently.
Also, someone suggested me to try and recreate the functions returning the table as well inside a transaction, but that did not change anything: BEGIN; ALTER TABLE... CREATE OR UPDATE FUNCTION ... END; Thanks for your help so far! /Victor On Fri, Oct 9, 2015 at 10:49 PM, Adrian Klaver <adrian.kla...@aklaver.com> wrote: > On 10/09/2015 07:31 AM, Albe Laurenz wrote: > >> Adrian Klaver wrote: >> >>> For the reason why this is happening see: >>>>> >>>>> >>>>> http://www.postgresql.org/docs/9.4/interactive/plpgsql-implementation.html#PLPGSQL-PLAN-CACHING >>>>> >>>> >>>> Yes, but the ALTER TABLE causes the plan to be recreated the next time. >>>> >>> >>> But does it? From the link above: >>> >>> "Because PL/pgSQL saves prepared statements and sometimes execution >>> plans in this way, SQL commands that appear directly in a PL/pgSQL >>> function must refer to the same tables and columns on every execution; >>> that is, you cannot use a parameter as the name of a table or column in >>> an SQL command. To get around this restriction, you can construct >>> dynamic commands using the PL/pgSQL EXECUTE statement — at the price of >>> performing new parse analysis and constructing a new execution plan on >>> every execution." >>> >>> I see '*' as a parameter. Or to put it another way '*' is not referring >>> to the same thing on each execution when you change the table definition >>> under the function. Now if I can only get the brain to wake up I could >>> find the post where Tom Lane explained this more coherently then I can:) >>> >> >> Session 1: >> >> test=> CREATE TABLE users (id integer PRIMARY KEY, name varchar NOT NULL, >> to_be_removed integer NOT NULL); >> CREATE TABLE >> test=> CREATE FUNCTION select_users(id_ integer) RETURNS SETOF users AS >> $$BEGIN RETURN QUERY SELECT * FROM users WHERE id = id_; END;$$ >> LANGUAGE plpgsql; >> CREATE FUNCTION >> >> Session 2: >> >> test=> SELECT id, name FROM select_users(18); >> id | name >> ----+------ >> (0 rows) >> >> Ok, now the plan is cached. >> >> Now in Session 1: >> >> test=> ALTER TABLE users DROP COLUMN to_be_removed; >> ALTER TABLE >> >> Session2: >> >> test=> SELECT id, name FROM select_users(18); >> id | name >> ----+------ >> (0 rows) >> >> No error. This is 9.4.4. >> > > I stand corrected. I also tried on Postgres 9.3.7, which is a close as I > could get to OP's 9.3.5 and it worked. Will have to rethink my assumptions. > > > >> Yours, >> Laurenz Albe >> >> > > -- > Adrian Klaver > adrian.kla...@aklaver.com >
