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I have 200 GB database in my production server.

System requirements: Amazon EC2 r4.2xlarge (8 vCPU,61 GB Memory)

I check, plan count with query:

SELECT objtype AS [CacheType]
        , count_big(*) AS [Total Plans]
        , sum(cast(size_in_bytes as decimal(18,2)))/1024/1024 AS [Total MBs]
        , avg(usecounts) AS [Avg Use Count]
        , sum(cast((CASE WHEN usecounts = 1 THEN size_in_bytes ELSE 0 END) as decimal(18,2)))/1024/1024 AS [Total MBs - USE Count 1]
        , sum(CASE WHEN usecounts = 1 THEN 1 ELSE 0 END) AS [Total Plans - USE Count 1]
FROM sys.dm_exec_cached_plans
GROUP BY objtype
ORDER BY [Total MBs - USE Count 1] DESC

Plan count are increasing over time, I saw total of 3K plans. 10-15 minutes later, I check plan count.

Total of plan count 200-600

Result:

enter image description here

enter image description here

Why is this happening?

I am not running DBCC FREEPROCCACHE.

Auto Close is false. I closed the parallisim and replication for a memory pressure. PLE 7600, but the values also fall from time to time.

I did not check how much space was used by the plans when they were 3K. But, I check now saw 900-1K plan and 250-300 mb. Then it is flushed.

Usually, query wait time is less than 1 sec. Average 200 ms. Top 3 wait type CXPACKET, CLR_AUTO_EVENT, SOS_SCHEDULER_YIELD.

I know about cache pressure limits (plans can be evicted due to memory pressure) but is it normal to do this often? Flushed for 2-3 minutes.

Microsoft SQL Server 2016 (SP1).

  • You've sort of answered your own question. You have 61 GB RAM and 200 GB data. When SQL Server needs RAM to cache query data or for query memory grants, it looks at cheaper caches like the plan cache to free up space. This could be a sign of memory pressure. If you run BlitzFirst with @SinceStartup = 1, what are your wait stats? – Erik Darling Jul 12 '17 at 7:29
  • See What keeps clearing my SQL Server plan cache? on Stack Overflow – SqlWorldWide Jul 12 '17 at 10:11
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SQL Server's max memory was set to default. I changed maximum memory to 90% (56240MB, total memory 61GB).

I think the problem is solved.

enter image description here

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