• The sql services got restarted by itself. It didn't failed over to other node. The services got restarted on the same instance. We tried to run the dbcc DROPCLEANBUFFERS but still the server got restarted on the same instance twice. After that it was back to normal. total memory on the server 500 GB , max memory setting for sql server 400. The memory got accumulated to around 200 GB and services got restarted. During this time we have seen dead locks happening on insert queries. Nothing much. Just backups and audit log jobs which load data from files to tables were running.