Johan De Meersman wrote:
First things first: You *are* on InnoDB, which has row-level locking instead of table-level ?
Yes, both "cli_lock" and "queue" tables are InnoDB. The server is running MySQL 5.1.36.
I find it strange that I would have so many of these deadlocks throughout a day when these queries run from 3 processes every 20 seconds. What's the chance that 2 scripts should be executing these queries simultaneously, and even if the probability exists, why is it causing this deadlock error each time?
If I break the query into 2 parts ... like SELECT FOR UPDATE followed by the INSERT/UPDATE, would that help fix the errors?
What is this error exactly, anyhow? Where is the deadlock ... is it on the select or the insert?
-- Dante
On Mon, Feb 1, 2010 at 4:08 PM, Michael Dykman <mdyk...@gmail.com <mailto:mdyk...@gmail.com>> wrote:The query is probably fine.. that is just the lock doing it's job. Take that advice literally.. when you fail with that class of exception, delay a milli-second or two and retry. For a large PHP site I designed, we had that behaviour built-in: up to three attempts waits 5, then 10 ms between trys. In spite of 1M+ user/day we rarely made it to the third attempt. - michael dykman On Mon, Feb 1, 2010 at 9:33 AM, Dante Lorenso <da...@lorenso.com <mailto:da...@lorenso.com>> wrote: > All, > > I am trying to create an atomic operation in MySQL that will manage a > "queue". I want to lock an item from a table for exclusive access by one of > my processing threads. I do this by inserting the unique ID of the record I > want to reserve into my "cli_lock" table. The following query is what I am > using to lock a record in my queue: > > INSERT INTO cli_lock (lock_id, object_id, lock_type, expire_dt) > SELECT $LOCK_ID, q.queue_id, 'parse', DATE_ADD(NOW(), INTERVAL 1 HOUR) > FROM queue q > LEFT JOIN cli_lock l ON l.object_id = q.queue_id AND l.lock_type = 'parse' > WHERE l.object_id IS NULL > AND q.status = 'parse' > ORDER BY q.file_size ASC, q.created ASC, q.queue_id ASC > LIMIT 1 > > However, as I execute this query several times each minute from different > applications, I frequently get these messages: > > DB ERROR: SQLSTATE[40001]: Serialization failure: 1213 Deadlock found when > trying to get lock; try restarting transaction > > Am I writing my query wrong or expecting behavior that MySQL doesn't > support? > > -- Dante >
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