SQL Server 环形缓冲区（Ring Buffer） -- RING BUFFER CONNECTIVITY 的深入理解
首先我们从连接的Ring Buffer数据返回的XML来入手。1
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SELECT CAST(record as xml) AS record_data
FROM sys.dm_os_ring_buffers
WHERE ring_buffer_type= 'RING_BUFFER_CONNECTIVITY'
执行上面的语句，得到下面的结果：
点击XML的超链接，打开文件内容看到更可读的内容，包括一条基本的Ring Buffer连接Error记录。
可以看到在XML文档中有许多相当有用的信息。像SniConsumerError，State和RemoteHost这些。
特别注意的是，RecordType节点，对于我们上面的截图来看标识为“Error”，说明是连接错误信息。为了识别这种类型的连接Ring Buffer，我们可以查询SniConsumerError代码号，准确定位是什么错误导致的。
RecordType包含那些值？
1. Error – 连接错误
2. LoginTimers – 连接超时
3. ConnectionClose – 杀掉进程
可以通过如下脚本，将XML数据转化为可读信息：
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;WITH RingBufferConnectivity as
( SELECT
records.record.value('(/Record/@id)', 'int') AS ,
records.record.value('(/Record/ConnectivityTraceRecord/RecordType)', 'varchar(max)') AS ,
records.record.value('(/Record/ConnectivityTraceRecord/RecordTime)', 'datetime') AS ,
records.record.value('(/Record/ConnectivityTraceRecord/SniConsumerError)', 'int') AS ,
records.record.value('(/Record/ConnectivityTraceRecord/State)', 'int') AS ,
records.record.value('(/Record/ConnectivityTraceRecord/Spid)', 'int') AS ,
records.record.value('(/Record/ConnectivityTraceRecord/RemoteHost)', 'varchar(max)') AS ,
records.record.value('(/Record/ConnectivityTraceRecord/RemotePort)', 'varchar(max)') AS ,
records.record.value('(/Record/ConnectivityTraceRecord/LocalHost)', 'varchar(max)') AS
FROM
( SELECT CAST(record as xml) AS record_data
FROM sys.dm_os_ring_buffers
WHERE ring_buffer_type= 'RING_BUFFER_CONNECTIVITY'
) TabA
CROSS APPLY record_data.nodes('//Record') AS records (record)
)
SELECT RBC.*, m.text
FROM RingBufferConnectivity RBC
LEFT JOIN sys.messages M ON
RBC.Error = M.message_id AND M.language_id = 1033
WHERE RBC.RecordType='Error' --Comment Out to see all RecordTypes
ORDER BY RBC.RecordTime DESC
执行上面的查询后，将得到下面的可读结果。在这个查询中，我们关联Ring Buffer数据和sys.messages视图去抓取Error id的文本。通过这个信息我们可以跟踪到精确的导致Error:Login失败的信息。
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