2009/12/7 黄晓骋 <huangxcl...@gmail.com>: > Hello, > > I think in Postgresql, concurrency control acts like this: > > tuple's infomask shows if it is being updated. If it is being updated now, > the latter transaction should reread the tuple and get the newer tuple. > During the progress of getting the newer tuple, it must use transaction > lock, I mean XactLockTableWait(...).
That is a table lock...depending on the lock, other backends may be allowed to update tuples in the relation still. Fine-grained tuple locks are used to prevent unnecessary contention for a table-wide lock. See the documentation at the manual page: http://www.postgresql.org/docs/8.4/static/explicit-locking.html It gives a thorough treatment of table and row locking levels and conflicts, as well as what gets what locks. fdr -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
