昨天網上一網友說，由於他同事誤將“max server memory”設置為10M后，SQL Server數據庫登錄不了，當時我簡單測試了一下，今天有空就順手將整個過程整理一下，記錄在此。
在SSMS的UI界面設置“max server memory”，即使你設置為10M大小，但是它會“悄悄”默認修改為128M，你用Profile跟蹤或者設置后會發現，它偷偷“修改”了你的設置值（改為了128M），
EXEC sys.sp_configure N'max server memory (MB)', N'128'
GO
RECONFIGURE WITH OVERRIDE
GO
Configuration option 'max server memory (MB)' changed from 4096 to 128. Run the RECONFIGURE statement to install.
如果你沒有注意這些細節，或者不信這個事情，那么也可以用腳本測試一下，如下所示，它提示你這個值（10M）不是一個有效值。
當你對“max server memory”做了錯誤設置后，那么基本上，任何查詢或連接都會出現類似下面這樣的錯誤：
An exception occurred while executing a Transact-SQL statement or batch. (Microsoft.SqlServer.ConnectionInfo)
------------------------------
There is insufficient system memory in resource pool 'internal' to run this query. (Microsoft SQL Server, Error: 701)
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ADDITIONAL INFORMATION:
A connection was successfully established with the server, but then an error occurred during the pre-login handshake. (provider: TCP Provider, error: 0 - 遠程主機強迫關閉了一個現有的連接。) (Microsoft SQL Server, Error: 10054)
For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft%20SQL%20Server&EvtSrc=MSSQLServer&EvtID=10054&LinkId=20476
------------------------------
遠程主機強迫關閉了一個現有的連接。
你檢查數據庫的錯誤日志，就會發現有很多額外信息，摘抄部分如下：
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2019-12-24 10:15:32.84 spid53 There is insufficient system memory in resource pool 'internal' to run this query.
2019-12-24 10:15:52.88 spid53 Error: 18056, Severity: 20, State: 29. (Params:). The error is printed in terse mode because there was error during formatting. Tracing, ETW, notifications etc are skipped.
2019-12-24 10:15:55.89 Server Error: 17300, Severity: 16, State: 1. (Params:). The error is printed in terse mode because there was error during formatting. Tracing, ETW, notifications etc are skipped.
2019-12-24 10:16:12.70 Server Failed allocate pages: FAIL_PAGE_ALLOCATION 1
2019-12-24 10:16:12.70 Server
Process/System Counts Value
---------------------------------------- ----------
Available Physical Memory 6614454272
Available Virtual Memory 140726213148672
Available Paging File 7776440320
Working Set 95432704
Percent of Committed Memory in WS 100
Page Faults 57030
System physical memory high 1
System physical memory low 0
Process physical memory low 1
Process virtual memory low 0
2019-12-24 10:16:12.70 Server
Memory Manager KB
---------------------------------------- ----------
VM Reserved 10652776
VM Committed 57972
Locked Pages Allocated 86472
Large Pages Allocated 0
Emergency Memory 1024
Emergency Memory In Use 16
Target Committed 131072
Current Committed 144448
Pages Allocated 84176
Pages Reserved 0
Pages Free 0
Pages In Use 144432
Page Alloc Potential -19912
NUMA Growth Phase 2
Last OOM Factor 1
Last OS Error 0
2019-12-24 10:16:12.70 Server
Memory node Id = 0 KB
---------------------------------------- ----------
VM Reserved 10652712
VM Committed 57952
Locked Pages Allocated 86472
Pages Allocated 84176
Pages Free 0
Target Committed 131048
Current Committed 144424
Foreign Committed 0
Away Committed 0
Taken Away Committed 0
2019-12-24 10:16:12.70 Server
Memory node Id = 64 KB
---------------------------------------- ----------
VM Reserved 0
VM Committed 20
Locked Pages Allocated 0
2019-12-24 10:16:12.70 Server
MEMORYCLERK_SQLGENERAL (node 0) KB
---------------------------------------- ----------
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要解決這個問題，你需要關閉數據庫服務， 然后以單用戶模式+最小配置啟動數據庫實例，然后去修改max server memory參數。 關閉數據庫過程中如果遇到一些問題，可以通過重啟服務器解決問題（這個要根據具體實際情況決定，有時候不會遇到問題，有時候會遇到一些問題，例如net stop mssqlserver命令卡住，出現service_state[MSSQLSERVER]): Stop pending）
注意：如果以單用戶模式啟動，然后以sqlcmd去連接數據庫，就會出現下面錯誤，所以必須以單用戶模式+最小配置啟動數據庫實例
EXEC sys.sp_configure 'max server memory (MB)',4096; #根據實際情況設置內存大小。
RECONFIGURE
GO
然后重啟SQL Server實例，問題就解決了。 當然你也可以還原master庫的備份到其它測試數據庫，然后用還原后master數據庫的相關文件替換當前數據庫master的相關文件來解決問題。但是那樣會相對麻煩，沒有這種方法簡便、有效！
C:\Windows\system32>net stop mssqlserver
The SQL Server (MSSQLSERVER) service is stopping.
The SQL Server (MSSQLSERVER) service was stopped successfully.
C:\Windows\system32>net start mssqlserver
The SQL Server (MSSQLSERVER) service is starting.
The SQL Server (MSSQLSERVER) service was started successfully.