![]() ![]() Rerun the transaction" appears instead of "Intra-query parallelism caused your server command (process ID #51) to deadlock. I guess the message "Transaction (Process ID 55) was deadlocked on lock | communication buffer resources with another process and has been chosen as the deadlock victim. The deadlock graph for one of these I've seen included a set of processes with only one SPID and a graph of objectlocks and exchangeEvents. Parallelism-related waits show up in SQL DMVs as CXPACKET or EXCHANGE wait types (note that the presence of these wait types is normal and simply indicates the presence of parallel query execution - by themselves, these waits don't indicate that this type or any other type of deadlock is occurring). Intra-query parallel requires signaling between these worker threads: the consumers may have to wait on producers to hand them more data, and the producers may have to wait for consumers to finish processing the last batch of data. There are "producer" threads that do the grunt work and feed sets of rows to "consumers". The idea is that the work for an operation like a large scan, sort, or join is divided up so that it can be executed on multiple child threads. These are described further in where the relevant paragraph is:Īn "exchangeEvent" resource indicates the presence of parallelism operators in a query plan. "Lock resources" are ordinary object locks, and "Communication Buffer resources" are exchangeEvents used for combining results of parallel queries. ![]() This provides all the information we need to identify the root cause of the deadlock and take necessary steps to resolve the issue.I would interpret the message as a deadlock on some combination of Lock resources or Communication Buffer resources. You can save the Deadlock xml as xdl to view the Deadlock Diagram. SELECT CAST(event_data AS XML) AS įROM sys.fn_xe_telemetry_blob_target_read_file('dl', These queries identifies the deadlock event time as well as the deadlock event details. Next logical question is, what caused this deadlock. So we have identified Deadlock happened in the database through our Application Insights. | communication buffer resources with another process and has been chosen as the deadlock victim. Transaction (Process ID 166) was deadlocked on lock Customize the degree of parallelism, or set it to 1 to execute in sequence. Log App Concurrency Control Behaviorįor each loops execute in parallel by default. The solution we implemented to alleviate this problem is to run this process in Sequence instead of parallel threads. That’s the root cause of the problem and we didn’t want to remove the explicit Transaction. Our process high percentage of shared data and we wanted to ensure the consistency, so we had Explicit Transactions in our Stored procedure calls. In Ideal world, Database should be able to handle numerous concurrent functions without deadlocks. The problem was Azure Functions invoked Database Calls which caused Deadlocks. So Logic App invoked several concurrent threads which in turn invoked several Azure Functions. Recently we were working with Azure Logic Apps to invoke Azure Functions.īy Default, Logic App runs parallel threads and we didn’t explicitly control the concurrency and left the default values. ![]()
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