ASYNC_NETWORK_IO wait stats mean SQL Server has results ready and is waiting for the application to read them. On Night 21 at the Clipboard Diner, hot plates pile up at the pass while Quinn tells a long story at table 4. Learn the causes in the order I find them, two queries that name the slow program, and why the fixes live in the application.
MSQL_XP Wait Stats: Extended Procedures and External Code
MSQL_XP wait stats measure the time a query waits while an extended stored procedure such as xp_cmdshell or xp_dirtree runs. On Night 20 at the Clipboard Diner, an outside caterer takes over one station behind a curtain. Then two queries show you which session is waiting and which procedure it called, and the fixes move that work outside SQL Server.
PREEMPTIVE Wait Stats: Calls Outside SQL Server
PREEMPTIVE wait stats record the time a task spends in code outside SQL Server, such as a call into Windows. On Night 19 at the Clipboard Diner, Kit picks up the wall phone to town hall and steps off the kitchen’s schedule. Then two queries find the preemptive waits that matter on your server.
LOGBUFFER Wait Stats: When the Log Buffer Fills
LOGBUFFER wait stats mean a task is waiting for free space in the log buffer before it can write a log record. On Night 18 at the Clipboard Diner, Pat’s notepad fills up faster than Pat can copy it into the order book. Then two queries show whether your log can keep up, and the fixes in order.
EXISTS: A Row Containing NULL Still Exists
EXISTS answers whether qualifying rows exist. Keep missing values separate from missing rows and preserve the intended correlation.
WRITELOG Wait Stats: Transaction Log Flush Waits
WRITELOG wait stats measure the time a commit waits for its log records to reach the disk. On Night 17 at the Clipboard Diner, Pat’s pen slows down and plates pile up at the pass. Then two queries show your log write latency, and a short script shows why many tiny commits hurt.
THREADPOOL Wait Stats: When Worker Threads Run Out
THREADPOOL wait stats mean a task is waiting for a worker thread because every worker is already busy. On Night 16 at the Clipboard Diner, every cook holds a ticket that can’t move, and nobody is free to take a new order. Then two queries show how close your server is to its worker limit, and how to get in when nobody else can.