Can You Optimize XML Operations in SQL Server? - sql-server

Question

I am generating & sending XML EVENTS from the database through a SQL BROKER using SQL CLR - and it works great. However, I am looking at the SQL PLAN and am a little shocked at some of the statistics. Small transformations seem to cost quite a bit of CPU TIME.
All the examples I see online optimize the TABLE the XML sits in by adding an index (etc)...but there is no table for me (I am simply generating the XML).
As such...
Q: Is there a way to "optimize" these kind of "generational" statements?
Maybe some approaches are better than others?
I have yet to see anything online about this
Thanks.
SAMPLES OF EXPENSIVE STATEMENTS:
DECLARE #CurrentId UNIQUEIDENTIFIER = (SELECT #Event.value('(/Event/#auditId)[1]', 'UNIQUEIDENTIFIER'));
SET #Event.modify('replace value of (/Event/#auditId)[1][1] with sql:variable("#NewId")');
EVENT XML:
An event would look like...
<Event auditId="FE4D0A4C-388B-E611-9B4D-0050569B733D" force="false" CreatedOn="2016-10-05T20:14:20.020">
<DataSource machineName="ABC123">DatabaseName</DataSource>
<Topic>
<Filter>TOPIC/ENTITY/ACTION</Filter>
</Topic>
<Name>Something.Created</Name>
<Contexts>
<Context>
<Name>TableName</Name>
<Key>
<IssueId>000</IssueId>
</Key>
</Context>
</Contexts>
</Event>

Answer 1

An XML index will not help you with this (Read this). There are very rare situations, where this kind of index would help you. The effect is high, if you read from your XML with full-path. In the moment you are using XQuery, any kind of navigation, it makes things even worse.
.modify() is quite heavy. In this special case it could be faster to rebuild the XML as such (you know more about it than the engine does):
DECLARE #xml XML=N'
<Event auditId="FE4D0A4C-388B-E611-9B4D-0050569B733D" force="false" CreatedOn="2016-10-05T20:14:20.020">
<DataSource machineName="ABC123">DatabaseName</DataSource>
<Topic>
<Filter>TOPIC/ENTITY/ACTION</Filter>
</Topic>
<Name>Something.Created</Name>
<Contexts>
<Context>
<Name>TableName</Name>
<Key>
<IssueId>000</IssueId>
</Key>
</Context>
</Contexts>
</Event>';
DECLARE #NewId UNIQUEIDENTIFIER=NEWID();
SELECT #NewId AS [#auditId]
,e.value('#force','nvarchar(max)') AS [#force] --read this as string to avoid expensive conversions
,e.value('#CreatedOn','nvarchar(max)') AS [#CreatedOn] --same here
,e.query('*') AS [node()] --read "as-is"
FROM #xml.nodes('/Event') AS A(e)
FOR XML PATH('Event');
There is - for sure! - no general approach to get XML things faster. If this existed, it would be the one and only ...
I'd monitor the system and pick out the most expensive calls and try to modify them one by one...