SQL LiteSpeed Error: XML returned from Engine was invalid
This is a very common error returned from SQL LiteSpeed. So what does it actually mean? What is the root cause?
What does it mean?
It means exactly what you think it means. When you first see it, you think, I don't know what that means," and that's exactly what it means. It's SQL LiteSpeed's way of saying, "I don't know what that means."
In other words, something was returned to SQL LiteSpeed from SQL Server that LiteSpeed doesn't understand or know how to handle. So, in essence, it's LiteSpeed's way of saying, "huh?".
Okay, so what is the root cause?
LiteSpeed may not know understand what's going on, but SQL Server probably does. You should be able to find an error in the SQL log at the same time that the LiteSpeed error occurred. Find the error to see what really happened.
For more info on how to query the SQL log, see this article on SQL log basics.
Now that you know what is wrong, go fix it.
For example....
I experienced this error recently when restoring a large (1.7 TB) database to another server. I checked the SQL log and found the following very interesting errors that clearly indicated that the server was experiencing issues with SAN connections or SAN throughput on the M drive:
SQL Server has encountered 1 occurrence(s) of I/O requests taking longer than 15 seconds to complete on file [M:\MSSQL\Data\<name censored>.NDF] in database [<Database name is not available>] (5). The OS file handle is 0x000000000000096C. The offset of the latest long I/O is: 0x0000298db90000
BackupVirtualDeviceFile::ClearError: failure on backup device 'VDI_17F16683-D4F6-4B46-BDBB-81D161A46DD6_1'. Operating system error 995(The I/O operation has been aborted because of either a thread exit or an application request.).
Error: 18210, Severity: 16, State: 1.
Error: 18210, Severity: 16, State: 1.
Followed by a dozen or so of these errors:
BackupIoRequest::WaitForIoCompletion: read failure on backup device 'VDI_17F16683-D4F6-4B46-BDBB-81D161A46DD6_5'. Operating system error 995(The I/O operation has been aborted because of either a thread exit or an application request.).
Error: 18210, Severity: 16, State: 1.
Error: 18210, Severity: 16, State: 1.
BackupMedium::ReportIoError: read failure on backup device 'VDI_17F16683-D4F6-4B46-BDBB-81D161A46DD6_3'. Operating system error 995(The I/O operation has been aborted because of either a thread exit or an application request.).
Error: 18210, Severity: 16, State: 1.
