topic Re: Deadlock exceptions in Alfresco Archive

Deadlock exceptions

jorell — Mon, 04 Aug 2014 19:45:28 GMT

I've been seeing a lot of the below exceptions in my logs. I am running 5.15 with multiple servers running on a single database. Not sure what the cause is or how to debug this. Any idea?Error updating database. Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLTransactionRollbackException: Deadlock foun

Re: Deadlock exceptions

frederikherema1 — Wed, 06 Aug 2014 08:42:03 GMT

What is the transaction isolation level? MySQL may do row-locking, depending on the isolation level of you're transactions. if multiple servers try to update a variable in the same process, this can result in deadlocks. If it's a different process-instance, MySQL is doing full-table-locks…

Re: Deadlock exceptions

jorell — Fri, 08 Aug 2014 16:19:56 GMT

The isolation level is Read uncommitted. Mysql shouldn't be doing full table locks for this isolation level. Also are these deadlocks anything I need to be concerned with or would Activiti roll back the transaction on its own and retry?

Re: Deadlock exceptions

frederikherema1 — Mon, 11 Aug 2014 07:34:28 GMT

Read uncommitted allows reading dirty rows in other ongoing uncommitted transactions. In order to get this behaviour consistent, I can imagine some locking going on (no separated snapshots of data in reads/writes, so SOMETHING needs to be locked at some point). I'm not a DBA, so I can only guess what's going on - IMHO, the READ UNCOMMITTED is causing this.

Activiti will rollback the transaction. In case the API-call was initiated from you're code, you'll get an ActivitiException and need to retry it yourself. In case the deadlocked occurred while executing a job (a timer that fired, an async activity that's executed), the deadlock will be caught and reported in the ACT_RU_JOB table (Job entity) and retried when the next executor slot is available. This will be attempted by default 3 times (configurable), until the retries are given up and the job is asleep. The job won't be deleted, rather it's present in the table with a retry-count of 0, allowing you to execute it manually raise the retry-count again using the API.