SQL 查询 XML 在 2000 年运行良好，在 2008 年 R2 运行缓慢

Question

I'm converting a client's SSIS packages from DTS to SSIS. In one of their packages they have an execute SQL task that has a query similar to this:

SELECT * FROM [SOME_TABLE] AS ReturnValues 
ORDER BY IDNumber
FOR XML AUTO, ELEMENTS

This query seems to return in a decent amount of time on the old system but on the new box it takes up to 18 minutes to run the query in SSMS. Sometimes if I run it it will generate an XML link and if I click on it to view the XML its throwing a 'System.OutOfMemoryException' and suggests increasing the number of characters retrieved from the server for XML data. I increased the option to unlimited and still getting error.

The table itself contains 220,500 rows but the query rows returned is showing 129,810 before query stops. Is this simply a matter of not having enough memory available to the system? This box has 48 GB (Win 2008 R2 EE x64), instance capped to 18GB because its shared dev environment. Any help/insight would be greatly appreciated as I don't really know XML!

Answer 1

When you are using SSMS to do XML queries FOR XML, it will generate all the XML and then put it into the grid and allow you to click on it. There are limits to how much data it brings back and with 220,000 rows, depending on how wide the table is, is huge and produces a lot of text.

The out of memory is the fact that SQL Server is trying to parse all of it and that is a lot of memory consumption for SSMS.

You can try to execute to a file and see what you get for size. But the major reason for running out of memory, is because that is a lot of XML and returning it to the grid, you will not get all the results all the time with this type of result set (size wise).

DBADuck (Ben)

Answer 2

The out of memory exception you're hitting is due to the amount of text a .net grid control can handle. 220k lines is huge. the setting in SSMS to show unlimited data is only as good as the .net control memory cap.

Answer 3

You coul look at removing the ELEMENTS option and look at the data in attribute format. That will decreate the amount XML "string space" returned. Personally, I prefer attributes over elements for that reason alone. Context is king, so it depends on what you're trying to accomplish (look at the data or use the data). Could youp pipe the data into an XML variable? When all is said & done, DBADuck is 100% correct in his statement.

SqlNightOwl