Merge pull request #2692 from alihacks/blitzlock-fix-memory-grant

sp_blitzLock results in excessive memory grant

Author: BrentOzar

sp_BlitzLock.sql

@@ -187,7 +187,7 @@ You need to use an Azure storage account, and the path has to look like this: ht
 			finding NVARCHAR(4000)
 		);
 
-		DECLARE @d VARCHAR(40), @StringToExecute NVARCHAR(4000),@StringToExecuteParams NVARCHAR(500),@r NVARCHAR(200),@OutputTableFindings NVARCHAR(100);
+		DECLARE @d VARCHAR(40), @StringToExecute NVARCHAR(4000),@StringToExecuteParams NVARCHAR(500),@r NVARCHAR(200),@OutputTableFindings NVARCHAR(100),@DeadlockCount INT;
 		DECLARE @ServerName NVARCHAR(256)
 		DECLARE @OutputDatabaseCheck BIT;
 		SET @d = CONVERT(VARCHAR(40), GETDATE(), 109);
@@ -309,17 +309,30 @@ You need to use an Azure storage account, and the path has to look like this: ht
         WITH xml
         AS ( SELECT CONVERT(XML, event_data) AS deadlock_xml
              FROM   sys.fn_xe_file_target_read_file(@EventSessionPath, NULL, NULL, NULL) )
-        SELECT TOP ( @Top ) ISNULL(xml.deadlock_xml, '') AS deadlock_xml
+        SELECT ISNULL(xml.deadlock_xml, '') AS deadlock_xml
         INTO   #deadlock_data
         FROM   xml
         LEFT JOIN #t AS t
         ON 1 = 1
-        WHERE  xml.deadlock_xml.value('(/event/@name)[1]', 'VARCHAR(256)') = 'xml_deadlock_report'
+        CROSS APPLY xml.deadlock_xml.nodes('/event/@name') AS x(c)
+        WHERE  1 = 1 
+        AND    x.c.exist('/event/@name[ .= "xml_deadlock_report"]') = 1
         AND    CONVERT(datetime, SWITCHOFFSET(CONVERT(datetimeoffset, xml.deadlock_xml.value('(/event/@timestamp)[1]', 'datetime') ), DATENAME(TzOffset, SYSDATETIMEOFFSET())))  > @StartDate
         AND    CONVERT(datetime, SWITCHOFFSET(CONVERT(datetimeoffset, xml.deadlock_xml.value('(/event/@timestamp)[1]', 'datetime') ), DATENAME(TzOffset, SYSDATETIMEOFFSET())))  < @EndDate
 		ORDER BY xml.deadlock_xml.value('(/event/@timestamp)[1]', 'datetime') DESC
 		OPTION ( RECOMPILE );
 
+		/*Optimization: if we got back more rows than @Top, remove them. This seems to be better than using @Top in the query above as that results in excessive memory grant*/
+		SET @DeadlockCount = @@ROWCOUNT
+		IF( @Top < @DeadlockCount ) BEGIN
+			WITH T
+			AS (
+				SELECT TOP ( @DeadlockCount - @Top) *
+				FROM   #deadlock_data
+				ORDER  BY #deadlock_data.deadlock_xml.value('(/event/@timestamp)[1]', 'datetime') ASC)
+			DELETE FROM T 
+		END
+
 		/*Parse process and input buffer XML*/
         SET @d = CONVERT(VARCHAR(40), GETDATE(), 109);
         RAISERROR('Parse process and input buffer XML %s', 0, 1, @d) WITH NOWAIT;