On 04/30/2017 11:54 PM, Philippe BEAUDOIN wrote:
Hi all,
I am coding an update script for an extension. And I am in trouble when
trying to rename a column of an existing table.
Just after the ALTER TABLE statement, I want to access this table. But
at this time, the altered column is not visible with its new name.
From the error it looks to me like the statements are each run in a
separate session and the UPDATE is not seeing the ALTER TABLE. A quick
search of the source indicates this is handled in extension.c:
https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/commands/extension.c;h=33b0de0a7657298729ad5c3b185dc2f4aab0bb73;hb=6a18e4bc2d13d077c52cf90a4c6ec68343808ba7
In particular execute_sql_string line 684. I do not understand C well
enough to figure out if the above is actually creating separate sessions
or not. Maybe you understand it or someone else can chime in.
# issue in postgres extension when trying to access a column that has
been renamed inside an extension update script
#
export EXTDIR="/tmp"
export PGDIR="/usr/local/pg962/share/postgresql/extension"
export PGHOST=localhost
export PGPORT=5496
export PGDATABASE='postgres'
echo "create files for the extension"
echo "------------------------------"
cat >$EXTDIR/myextension.control <<*END*
default_version = '1'
directory = '$EXTDIR'
*END*
sudo ln -s $EXTDIR/myextension.control $PGDIR/myextension.control
cat >$EXTDIR/myextension--1.sql <<*END*
CREATE TABLE mytable (col_old INT);
*END*
cat >$EXTDIR/myextension--1--2.sql <<*END*
ALTER TABLE mytable RENAME col_old TO col_new;
UPDATE mytable SET col_new = 0;
*END*
echo "psql: run the test ==> FAILS"
echo "----------------------------"
psql -a <<*END*
select version();
CREATE EXTENSION myextension VERSION '1';
ALTER EXTENSION myextension UPDATE TO '2';
DROP EXTENSION IF EXISTS myextension;
*END*
echo "psql: similar statements outside extension ==> WORKS"
echo "----------------------------------------------------"
psql -a <<*END*
CREATE TABLE mytable (col_old INT);
BEGIN;
ALTER TABLE mytable RENAME col_old TO col_new;
UPDATE mytable SET col_new = 0;
COMMIT;
DROP TABLE IF EXISTS mytable;
*END*
sudo rm $PGDIR/myextension.control
rm $EXTDIR/myextension*
And here is the result:
create files for the extension
------------------------------
psql: run the test ==> FAILS
----------------------------
select version();
version
-----------------------------------------------------------------------------------------------------------------
PostgreSQL 9.6.2 on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu
5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609, 64-bit
(1 row)
CREATE EXTENSION myextension VERSION '1';
CREATE EXTENSION
ALTER EXTENSION myextension UPDATE TO '2';
ERROR: column "col_new" of relation "mytable" does not exist
DROP EXTENSION IF EXISTS myextension;
DROP EXTENSION
psql: similar statements outside extension ==> WORKS
----------------------------------------------------
CREATE TABLE mytable (col_old INT);
CREATE TABLE
BEGIN;
BEGIN
ALTER TABLE mytable RENAME col_old TO col_new;
ALTER TABLE
UPDATE mytable SET col_new = 0;
UPDATE 0
COMMIT;
COMMIT
DROP TABLE IF EXISTS mytable;
DROP TABLE
As you can see:
- the error message is "ERROR: column "col_new" of relation "mytable"
does not exist", while the ALTER TABLE statement doesn't return any error,
- the same statements in a simple psql script works fine,
- I reproduce this with all supported postgres versions.
As a workaround, I perform the UPDATE statement before the ALTER TABLE
operation, using of course the old column name.
I probably do something wrong. But I can't see what.
Thanks by advance for any piece of advise.
Best regards. Philippe Beaudoin.
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
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