Andy 2) Locks are by thread. If thread dies, so does it's lock.
David > -----Original Message----- > From: Andy Sy [mailto:[EMAIL PROTECTED]] > Sent: Wednesday, June 12, 2002 12:03 PM > To: [EMAIL PROTECTED] > Subject: Auto-increment across multiple tables / Atomicity of update > statements > > > In MySQL, > > I want to use an auto-incrementing value that works > across multiple tables. For example I have 3 tables > forumA, forumB, forumC, each of which has a primary > key field called 'msgnum'. However, if I declare > 'msgnum' auto_increment, 'msgnum' will not be > unique across the 3 tables. > > Thus, instead of using an auto_increment column, I > made an auxiliary table which will hold the last used > 'msgnum' and update it each time a new record is > inserted in any of the 3 tables. Since I plan to use > this auxiliary table to hold other values as well and > INSERTs to the 3 tables may happen extremely often, I > would rather not have the overhead of repeatedly LOCKing > and UNLOCKing the table. > > In connection with this, the following 2 issues crop > up: > > #1) Is the following statement guaranteed atomic? > > UPDATE TBL SET COL=COL+1 > > and is there anyway to retrieve the value of COL > that was last set by the connection that set it? > > #2) If a thread with a LOCK on a table unexpectedly dies > without being able to UNLOCK it, does it automatically > relinquish the lock? > > > > --------------------------------------------------------------------- > Before posting, please check: > http://www.mysql.com/manual.php (the manual) > http://lists.mysql.com/ (the list archive) > > To request this thread, e-mail <[EMAIL PROTECTED]> > To unsubscribe, e-mail > <[EMAIL PROTECTED]> > Trouble unsubscribing? Try: http://lists.mysql.com/php/unsubscribe.php > --------------------------------------------------------------------- Before posting, please check: http://www.mysql.com/manual.php (the manual) http://lists.mysql.com/ (the list archive) To request this thread, e-mail <[EMAIL PROTECTED]> To unsubscribe, e-mail <[EMAIL PROTECTED]> Trouble unsubscribing? Try: http://lists.mysql.com/php/unsubscribe.php
