This script lock in the update statement following select for update:
eng=sqlalchemy.create_engine('postgres://x.loc/db')
metadata=sqlalchemy.MetaData()
metadata.bind=eng
tab1 = Table('tab1', metadata, autoload=True)
a_rec =
tab1.select( for_update=True ).where(the_condition).execute().fetchone()
tab1.update().where(new_condition).values(stato = 'DEL').execute()
After select this is pg_lock data:
relname | locktype | transaction | pid | mode
----------------+----------+-------------+-------+-----------------
tab1 | relation | 6788234 | 28293 | AccessShareLock
tab1 | relation | 6788234 | 28293 | RowShareLock
During update this is pg_lock data:
relname | locktype | transaction | pid | mode
----------------+----------+-------------+-------+------------------
tab1 | tuple | 6788240 | 28294 | ExclusiveLock
tab1 | relation | 6788234 | 28293 | AccessShareLock
tab1 | relation | 6788234 | 28293 | RowShareLock
tab1 | relation | 6788240 | 28294 | AccessShareLock
tab1 | relation | 6788240 | 28294 | RowExclusiveLock
Note: the script generate two different transactions.
What is wrong ?
An equivalent "psycopg2 only" script work fine.
Thanks.
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