The max_memory limit is set to 4Mb while the max_event limit is set to 5000 events for the system_health session The reason is that it either reaches the max_memory or max_events limit. Therefore, in the highly active servers it is possible that a large amount of events is 0.5MB in size which limits the available space in the system_health extended event ring_buffer for the deadlock events that are serialized to the XML format (serialized size can be over 4.5MB) so it doesn’t show up in the XEL (event file format) file up until it has been buffered out. To elaborate, the maximum memory assigned to the ring buffer is 4MB. This is not the most reliable method for collecting the deadlocks, and it cannot always be guaranteed that all deadlocks are captured or that deadlocks event might be available with severe delay. The system_health extended event is SQL Server native extended event that, among other information, collects data about the SQL Server deadlocks. The system health extended event – default option What is the difference between the ApexSQLMonitorDeadlock extended event and system_health extended event? See more information on the ApexSQLDeadlock extended event below To meet the various user preferences, ApexSQL Monitor utilizes two different approaches in the SQL Server deadlocks monitoring: using the SQL Server native system_health extended event or using the ApexSQL Monitor’s dedicated ApexSQLDeadlock extended event. How does ApexSQL Monitor collects SQL Server deadlocks data?ĪpexSQL Monitor SQL Server deadlock monitoring is entirely based on using SQL Server Extended Events.
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