SQL Server vNext: query_store_wait_stats

The missing link

Back when the Query Store first got announced, I was amazed.

The amount of information it gathered and persisted between reboots was such a big improvement over the plan cache, plus being able to force plans was really cool.

I was always surprised that wait stats weren’t a part of that, especially with 2016 adding session level wait stats, and run time info to Extended Events and Query Plans.

After all, wait stats really are the bread and butter of troubleshooting SQL Server bottlenecks.

SQL Server vNext

Or SQL Server 2017. Whatever. It adds a new Query Store DMV called query_store_wait_stats. So what’s in there?

Well, you know when you used to open up Activity Monitor, back before you learned how lousy Activity Monitor is?

Right now, that’s kind of what this DMV shows you.

Here’s my uninteresting Query Store query.

SELECT qsws.plan_id, 
     qsws.wait_stats_id, 
     qsrs.runtime_stats_interval_id,
     count_executions,
     qsws.wait_category_desc, 
     qsws.total_query_wait_time_ms, 
     qsws.avg_query_wait_time_ms, 
     qsws.last_query_wait_time_ms, 
     qsws.min_query_wait_time_ms, 
     qsws.max_query_wait_time_ms,
     qsqt.query_sql_text,
     x.actual_xml
FROM sys.query_store_wait_stats qsws
JOIN sys.query_store_plan AS qsp
ON qsws.plan_id = qsp.plan_id 
JOIN sys.query_store_runtime_stats AS qsrs
ON  qsrs.plan_id = qsp.plan_id
JOIN sys.query_store_query AS qsq
ON  qsq.query_id = qsp.query_id
JOIN sys.query_store_query_text AS qsqt
ON qsq.query_text_id = qsqt.query_text_id
CROSS APPLY ( SELECT TRY_CONVERT( XML, qsp.query_plan) AS actual_xml ) AS x
WHERE qsws.plan_id = 62
AND qsrs.execution_type = 0

And here are the results.

Descriptive

There’s a wait_stats_id column, but I don’t see that it maps to anything right now. I was hoping that it mapped to Extended Events wait stats map keys, but it doesn’t appear to.

  SELECT dxmv.map_key, dxmv.map_value
  FROM sys.dm_xe_map_values AS dxmv
  WHERE dxmv.name = 'wait_types'
  ORDER BY map_key

So for now, you just have to take the description of the wait stats for what they are until there’s something to link the actual wait types to.

But still, this is really cool, and a great step towards making Query Store a total performance troubleshooting and profiling tool.

Thanks for reading!

Brent says: to guess what it might map to, I checked sys.all_columns looking for names like ‘%wait%’ and like ‘%id%’, and I didn’t get a good answer – but I came up with another question. There’s something called sys.plan_persist_wait_stats, and it doesn’t appear to be documented anywhere yet. Hmm.

The Internet ends here at plan_persist_wait_stats

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