今天遇到了Reporting Services（SQL SERVER 2008 R2）的报表执行异常情况，报表加载数据很长时间都没有响应，最后报“An error occurred within the report server database. This may be due to a connection failure, timeout or low disk condition within the database.;”。检查C:\Program Files\Microsoft SQL Server\MSRS10_50.MSSQLSERVER\Reporting Services\LogFiles下日志，发现ReportServerService__12_24_2014_10_29_02.log中有大量如下错误：
library!WindowsService_4!1308!12/24/2014-01:27:53:: ;i INFO: Call to CleanBatch() library!WindowsService_4!1308!12/24/2014-01:32:53:: ;e ERROR: Throwing Microsoft.ReportingServices.Diagnostics.Utilities.ReportServerStorageException: , An error occurred within the report server database. This may be due to a connection failure, timeout or low disk condition within the database.; dbcleanup!WindowsService_4!1308!12/24/2014-01:32:53:: ;e ERROR: Sql Error in CleanOrphanedSnapshots: Microsoft.ReportingServices.Diagnostics.Utilities.ReportServerStorageException: An error occurred within the report server database. This may be due to a connection failure, timeout or low disk condition within the database. ---> System.Data.SqlClient.SqlException: Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding. library!WindowsService_4!1308!12/24/2014-01:32:53:: ;i INFO: Cleaned 0 batch records, 0 policies, 0 sessions, 0 cache entries, 0 snapshots, 0 chunks, 0 running jobs, 0 persisted streams, 0 segments, 0 segment mappings, 0 edit sessions. library!WindowsService_4!1308!12/24/2014-01:32:53:: ;i INFO: Call to CleanBatch() ends library!WindowsService_4!13ec!12/24/2014-01:37:53:: ;i INFO: Call to CleanBatch() library!WindowsService_4!13ec!12/24/2014-01:42:53:: ;e ERROR: Throwing Microsoft.ReportingServices.Diagnostics.Utilities.ReportServerStorageException: , An error occurred within the report server database. This may be due to a connection failure, timeout or low disk condition within the database.; dbcleanup!WindowsService_4!13ec!12/24/2014-01:42:53:: ;e ERROR: Sql Error in CleanOrphanedSnapshots: Microsoft.ReportingServices.Diagnostics.Utilities.ReportServerStorageException: An error occurred within the report server database. This may be due to a connection failure, timeout or low disk condition within the database. ---> System.Data.SqlClient.SqlException: Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding. library!WindowsService_4!13ec!12/24/2014-01:42:53:: ;i INFO: Cleaned 0 batch records, 0 policies, 0 sessions, 0 cache entries, 0 snapshots, 0 chunks, 0 running jobs, 0 persisted streams, 0 segments, 0 segment mappings, 0 edit sessions. library!WindowsService_4!13ec!12/24/2014-01:42:53:: ;i INFO: Call to CleanBatch() ends library!WindowsService_4!1308!12/24/2014-01:47:53:: ;i INFO: Call to CleanBatch() library!WindowsService_4!1308!12/24/2014-01:52:53:: ;e ERROR: Throwing Microsoft.ReportingServices.Diagnostics.Utilities.ReportServerStorageException: , An error occurred within the report server database. This may be due to a connection failure, timeout or low disk condition within the database.; dbcleanup!WindowsService_4!1308!12/24/2014-01:52:53:: ;e ERROR: Sql Error in CleanOrphanedSnapshots: Microsoft.ReportingServices.Diagnostics.Utilities.ReportServerStorageException: An error occurred within the report server database. This may be due to a connection failure, timeout or low disk condition within the database. ---> System.Data.SqlClient.SqlException: Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding. library!WindowsService_4!1308!12/24/2014-01:52:53:: ;i INFO: Cleaned 0 batch records, 0 policies, 0 sessions, 0 cache entries, 0 snapshots, 0 chunks, 0 running jobs, 0 persisted streams, 0 segments, 0 segment mappings, 0 edit sessions. library!WindowsService_4!1308!12/24/2014-01:52:53:: ;i INFO: Call to CleanBatch() ends
检查了服务器的存储情况后，可以排除low disk问题，只能是connection failure, timeout的问题，于是我查看1点多的执行记录，发现取数据时间都是几百秒，如下截图所示
我检查C:\Program Files\Microsoft SQL Server\MSRS10_50.MSSQLSERVER\Reporting Services\ReportServer下的rsreportserver.config,发现DatabaseQueryTimeout为120秒
但是这些报表的SQL语句我在SSMS里面执行过，也只有1~2秒，根本不会超时的情况。当时我立马重启了SSRS服务后，问题解决。那么问题究竟出自哪里呢？搜索了网上很多资料，大致有下面一些原因：
原因1：SSRS服务崩溃了，不能响应用户请求。
These threads could help: SSRS 2008 crashing when running a report with huge amount of data long running report can not be rendered in Report Manager .....
- SSRS 2008 crashing when running a report with huge amount of data
- long running report can not be rendered in Report Manager or through Subscription
具体可以参见“参考资料”选URL中的讨论。
原因2：Database deadlocks occur when you try to view an SSRS report in the SharePoint integrated mode after you update a data source
具体可以参考官方文档http://support.microsoft.com/kb/2691331/en-us ，不过由于我们服务器并没有应用SharePoint integrated mode，所以应该可以排除。
原因3：Cannot rename a report in SharePoint integrated mode.这个核查过后，也可以排除。
至此，由于第一次遇到这个错误，搜索了大量资料也没有看到一个很明确的答案，加之SSRS确实也是问题多多。所以我觉得应该是SSRS服务崩溃了。如有不对，敬请指出。
参考资料：
http://support.microsoft.com/kb/2691331/en-us
http://blog.davyknuysen.be/2010/09/22/cannot-rename-a-report-in-sharepoint-integrated-mode/