Ludwig Lim <[EMAIL PROTECTED]> writes: > *** For clarification ***
> In the SQL command reference of PostgreSQL: > in SELECT statement section : > "The FOR UPDATE clause allows the SELECT > statement to perform exclusive locking of selected > rows" Hmm. That is a misstatement: FOR UPDATE only locks the selected row(s) against other updates (ie UPDATE, DELETE, SELECT FOR UPDATE), so it's not "exclusive" in the usual sense of the word: readers can still see the row. I'll fix that for 7.3, but meanwhile you might care to read the 7.3 development docs' discussion of concurrency, which is (IMHO anyway) more accurate than what was there before: http://developer.postgresql.org/docs/postgres/mvcc.html Note in particular that table-level locks and row-level locks are two independent features. Updates acquire an appropriate table-level lock and then acquire row locks on the rows they are updating. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
