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Re: Implementing rowlocking

by themage (Friar)
on Jan 09, 2007 at 09:38 UTC ( #593684=note: print w/replies, xml ) Need Help??

in reply to Implementing rowlocking

Hi oyse,

Using autocommit or not is irrelevant in your present situation as it would not prevent the the lock row from being inserted in another transaction at the same time.

What you really nead is to LOCK your lock table:
mysql> LOCK TABLE locks WRITE; mysql> SELECT * FROM locks where yourcond=true; mysql> INSERT locks (...) VALUES(...); mysql> UNLOCK TABLES;
Some notes:
  • Don't forget to unlock the table, specially if your server is using persistent connections, like with Apache::DBI or pconnect in php, or no other connection will ever can lock the table.
  • You can use LOCK TABLE locks READ if you just need to read the table, but you should use the WRITE lock for the select and the insert, or another thread can write after you read.
  • Any connection that don't LOCK the table before attempting to do anything with it will success indepedently of the locks(, so you need to use the lock in every operation on this table).
  • You should not do any operation that takes long (0.01+ secs) with LOCKS, as only one thread can LOCK the table at any time.
  • All tables used after a lock and before an unlock must be locked.

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