问题
I need a simple table that acts as a Queue. My MySQL server restriction is I can't use InnoDB tables, only MyISAM.
Clients/workers will work at the same time and they will need to receive differents jobs each time.
My idea is to do the following (pseudo-code):
$job <- SELECT * FROM queue ORDER BY last_pop ASC LIMIT 1;
UPDATE queue SET last_pop WHERE id = $job->id
return $job
I had tried table lock and "GET_LOCK" but nothing happends, workers sometimes receives same jobs.
回答1:
You need to turn your ordering around so there is no timing window.
Consumer POP (each consumer has a unique $consumer_id)
Update queue
set last_pop = '$consumer_id'
where last_pop is null
order by id limit 1;
$job =
Select * from queue
where last_pop = '$consumer_id'
order by id desc
limit 1;
Supplier PUSH
insert into queue
(id, last_pop, ...)
values
(NULL, NULL, ...);
The queue is ordered in time by the id column and assigned upon POP by to the consumer_id.
回答2:
Just for information, there's another option that is using Gearman instead of a table to make the queue: Rasmus Lerdorf wrote a very nice article about it.
回答3:
Oleg,
The solution is correct. $consumer_id must be a unique identifier for the processor. If you had a couple cron jobs on one machine, for example, you could use their pid as the consumer ID .
The UPDATE is atomic, so it marks exactly one row in the queue as being consumed by your ID.
For some applications I also have a status field for finished, so that if last_pop's consumer_id is set, but the finished flag is not set and the job is older than X, it can be marked to be restarted.
来源：https://stackoverflow.com/questions/1690748/php-mysql-queue