-> Client attempted to reclaim what he believes to be significant unused space in a datafile by running DBCC SHRINKFILE.
-> Shrinkfile process was running for over 39 hours. Client was not sure if it was a matter of just waiting, or if it is in a state where it will never complete.
-> I thought that DBCC Shrinkfile is supposed to take lot of time and I was under the impression that it is just a matter of waiting for the operation to complete.
-> I tried checking the process and wanted to confirm if it was progressing and then advise client to wait or just cancel it, as shrink file is not a recommended operation. Client advised me that they purged a huge table and this is an one time operation and it released close to 92% free space. Now they wanted to shrink it just for one time which makes sense.
-> I executed below query to check the progress of shrink operation and it showed that it is 100% complete. But the SPID was still active,
SELECT start_time, percent_complete, DATEADD (ss,DATEDIFF (ss,start_time,getdate()) / percent_complete * 100,start_time) AS Expected_end_time, st.text as SQL, command as Current_Command,session_id FROM sys.dm_exec_requests er CROSS APPLY sys.dm_exec_sql_text(er.sql_handle) st WHERE percent_complete != 0
-> Below was the screen grab of the shrink process,
-> DBCC Shrinkfile shows as 100% complete. But the process is blocked by SPID 48.
-> SPID 48 shows as NULL. DBCC Inputbuffer also returns NULL. Seems like this is a system process.
-> I stopped the shrinkfile and restarted it. It starts up without any issue. It progresses well, But as soon as it reaches 100% there is a blocking and is always blocked by this system process. This behavior is evident every time I start the Shrink operation on this data file.
-> More details on SPID 48 below,
-> Spid 48 seems to have a cmd type of “BRKR TASK” and wait type on that process is “BROKER_TRANSMISSION_TABLE”.
-> I did a guess that this system process should be related to Service broker. It seems like some operation related to Servcie Broker is not letting Shrink operation to complete.
-> Executed Sp_Lock and below was the details,
-> From the above screenshot it is clear that these 2 operations require access to object with objectID 73.
-> Object ID 73 is a system object sysdercv. This object exists in every database, contains a row for each receiving endpoint of a service broker conversation.
-> Object sys.conversation_endpoints has 197483543 rows. Out of which 169473219 rows are Started Outbound.
-> Started Outbound refers to SQL Server has processed a BEGIN Conversation, but no messages have yet been sent. Checking conversations in sys.conversation_endpoint for state STARTED_OUTBOUND.
-> Notice the lifetime for these entries, these entries can be reclaimed only after the lifetime message.
-> Advised Client to add a lifetime to every conversation. Below code adds a 120 seconds lifetime for each conversation,
begin dialog conversation @h from service [JB_SB_source] to service N'JB_SB_target' with encryption = off, lifetime = 120;
-> Also advised Client to add an END CONVERSATION in the code which handles the message.
-> Advised Client to execute below code to perform cleanup from sys.conversation_endpoints with state STARTED_OUTBOUND that has a lifetime value greater than 1 month from current date. Below code was copied from this article.
declare @h uniqueidentifier, @count int = 0; begin transaction; while (1=1) begin set @h = null; select top(1) @h = conversation_handle from sys.conversation_endpoints where state_desc = N'STARTED_OUTBOUND' and security_timestamp = '1900-01-01 00:00:00.000' and lifetime > dateadd(month, 1, getutcdate()) if (@h is null) begin break end end conversation @h with cleanup; set @count += 1; if (@count > 1000) begin commit; set @count = 0; begin transaction; end end commit
-> After these changes DBCC SHRINKFILE completed fine without any issues.
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