Re: Lock a viewe

[Luis Marin <luismarinaray@xxxxxxxxx>]

Hi,

Have you tried,

https://wiki.postgresql.org/wiki/Lock_Monitoring

https://www.postgresql.org/docs/9.1/static/explicit-locking.html

https://www.postgresql.org/docs/9.1/static/sql-lock.html

Regards

2016-12-20 16:17 GMT-04:00 Gaetano Mendola <mendola@xxxxxxxxx>:

Hi,

I was wondering if there is a clean view to lock the usage of a view.

Basically during a schema migration, with applications still running a typical
schema change is:

BEGIN;
ALTER TABLE x ADD COLUMN (a INTEGER);
CREATE OR REPLACE VIEW v_x
AS 
SELECT a,b FROM x;
COMMIT;

now the issue is that if an application performs a:

SELECT * from v_x;

between the ALTER and the view redefinition then a deadlock happens.

I'm preventing this issue doing a:

ALTER VIEW v_x ALTER COLUMN b DROP DEFAULT; 

(anyway there was no default on the view)

before the ALTER TABLE, that's basically reorders the locks sequence
avoiding the dead lock.

Is there a clean way to achieve it without the "hack"?


GM