Parallel query worker thread was involved in a deadlock
deadlock, parallel-processing, sql, sql-server
Solution
Q1: No. This just means that the deadlock involves an Exchange operator. On the client side you'll get the error "Transaction (Process ID n) was deadlocked on {thread | communication buffer} resources with another process and has been chosen as the deadlock victim."
These kind of deadlock will always include two or more processes and will always include a lock resource.
Here is a repro for this scenario. In most cases, having the correct index will resolve this issue.
When a process deadlock with itself (very rare with latest builds) it's called Intra-Query Parallelism deadlock and you will get an error like "Msg 8650, Level 13, State 1, Line 1 Intra-query parallelism caused your server command (process ID n) to deadlock. Rerun the query without intra-query parallelism by using the query hint option (maxdop 1)." See this link for details.
Q2: Refer to the links Denis provided.
Problem
I run an SQL Server Trace to track some deadlocks issues and I was hit on the head with this comment `Parallel query worker thread was involved in a deadlock` as a reason for the deadlock. Q1: Does this means that the same query is deadlocking it self? The query execution plan shows some parallelism cases. Q2: What are the possible ways to "force" SQL Server not to use parallelism or at least to avoid using it as much as possible?