On Sat, 22 Jul 2006, Alvaro Herrera wrote:
Martin Marques escribió:
Is it posible to get an exclusive (read/write) lock on certain rows? I
don't want to block the whole table, only certain rows, but I want it to
be a read/write lock.
That's what SELECT FOR UPDATE does.
Hi Alvaro,
After the SELECT FOR UPDATE other transactions can still see the locked
rows. I want a read/write lock, so no one can access does rows.
AFAIK SELECT FOR UPDATE doesn't help with this.
Why?
trans1:
prueba2=> BEGIN;
BEGIN
prueba2=> SELECT * FROM personas FOR UPDATE;
codigo | nombre | apellido | tipodoc | docnum
--------+--------+----------+---------+----------
3 | Martin | Marques | 1 | 23622139
(1 row)
Meanwhile, at this moment trans2:
prueba2=> BEGIN;
BEGIN
prueba2=> SELECT * FROM personas;
codigo | nombre | apellido | tipodoc | docnum
--------+--------+----------+---------+----------
3 | Martin | Marques | 1 | 23622139
(1 row)
pg_locks shows the the lock is RowShareLock, so there is no read lock on
those rows, which is what I want.
--
21:50:04 up 2 days, 9:07, 0 users, load average: 0.92, 0.37, 0.18
---------------------------------------------------------
Lic. Martín Marqués | SELECT 'mmarques' ||
Centro de Telemática | '@' || 'unl.edu.ar';
Universidad Nacional | DBA, Programador,
del Litoral | Administrador
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