Re: InnoDB: Warning: a long semaphore wait:. X-lock on RW-latch

[Erik Morton]

The id column on orders is PRIMARY KEY. id on sessions is also PRIMARY KEY.

There was no index on the order_id column on the line_items table. The table only has 130,000 rows, but any time the application loaded an order it would scan the entire table for its line_items. The index has been added.

The UPDATE


I didn't kill any threads.

There are no queries that would join with sessions.

So does the following (from the error log) mean that the sessions table is indeed locked?

---TRANSACTION 0 2004317, ACTIVE 270 sec, process no 1440, OS thread id 1164314960 updating or deleting, thread declared inside InnoDB 499
mysql tables in use 1, locked 1
2 lock struct(s), heap size 368
MySQL thread id 107, query id 2118811 ip-10-250-59-241.ec2.internal 10.250.59.241 storefront Updating
UPDATE `sessions` SET `data` = '...', `updated_at` = '2008-12-23'

Thanks for the help. This is very useful.