Re: Question about tuple´s lock

Carlos Alves <carlos.alves@tecnisys.com.br> writes:
> I need some help to understand why a transaction wiht a row delete
> aquire a AccessExclusiveLock and a row update a ExclusiveLock. 

UPDATE can use the weaker lock type if it's not modifying any
column that is part of a unique index.  This is to allow concurrency
with foreign-key checks that might wish to grab a read-only (shared)
lock on such a tuple.

A DELETE, or an UPDATE that is modifying key columns, has to
conflict with foreign-key checks.

            regards, tom lane