Steve, ----- Original Message ----- From: ""Steve McWilliams"" <[EMAIL PROTECTED]> Newsgroups: mailing.database.mysql Sent: Wednesday, August 27, 2003 12:07 AM Subject: Question about row level locking with InnoDB tables
> Hello, > > I am relatively new to MySql (4.0.14) but I have read through the relevent > documentation and am still confused about how row level locking behaves > with InnoDB tables. > > I created a database with a single innodb table which has 2 columns, one > of which is indexed. The locking behavior I see when I test against this > database is that it uses row level locks if the "SELECT ... FOR UPDATE" > involves the indexed column, but uses table level locks if instead it > involves the non-indexed column. > > For example, if I have 2 mysql clients that perform the following operations: > > client1> set autocommit=0; > client1> begin; > client1> SELECT my_column FROM my_table WHERE my_column = 1 FOR UPDATE; > client2> set autocommit=0; > client2> begin: > client2> SELECT my_column FROM my_table WHERE my_column = 2 FOR UPDATE; > > The above query by client2 will block if the column in question is not > indexed, implying that client1 has somehow locked the entire table, even > though client1 and client2 are selecting different rows. a locking SELECT will set row locks (usually next-key locks) on every index record it looks at. This is necessary to prevent 'phantom rows' from appearing in your result set. If you do not have an index on my_column, MySQL needs to scan the whole table and thus it locks every row. http://www.innodb.com/ibman.html#Locks_set_by_statements http://www.innodb.com/ibman.html#Next_key_locking http://www.innodb.com/ibman.html#Cope_with_deadlocks > Am I misconfiguring something, or does InnoDB simply only support row > level locking when you are selecting indexed rows? > > Thanks in advance, > > Steve McWilliams > Software Engineer > Emprisa Networks > 703-691-0433x21 > [EMAIL PROTECTED] Best regards, Heikki Tuuri Innobase Oy http://www.innodb.com Foreign keys, transactions, and row level locking for MySQL InnoDB Hot Backup - a hot backup tool for MySQL Order MySQL technical support from https://order.mysql.com/ -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
