How to reduce cost of parsing small XML in SQL Server? - sql-server

Question

I have following T-SQL code:
DECLARE #DesiredCategories TABLE(CategoryID INT, Search BIT, SearchText NVARCHAR(50));
INSERT INTO #DesiredCategories
SELECT X.Col.query('id').value('.', 'INT') as CategoryID,
X.Col.value('#search', 'BIT') as Search,
X.Col.query('text').value('.', 'NVARCHAR(MAX)') as SearchText
FROM .nodes('root/node') X(Col);
#XMLCategoryIDs contains XML like this:
<root>
<node search="0"><id>10088</id><text></text></node>
<node search="0"><id>10087</id><text></text></node>
<node search="0"><id>10090</id><text></text></node>
</root>
Sadly, this code have very high subtree cost (for following code snippet it's ~900) and seems to be a perfomance bottleneck.
Execution plan is included - http://pastebin.com/ptnqJ4jX
We are using XML to send varying number of parameters (1-5) to stored procedure.
And yes, I'm total beginner with XML manipulation in SQL.

Answer 1

If your xml is stored in a table, you can create a primary xml index to reduce subtree cost for queries against that xml at a later time. You're basically shifting the workload to earlier in the process, but this might help your situation.
IF OBJECT_ID('tempdb..#Table') IS NOT NULL
DROP TABLE #Table;
CREATE TABLE #Table
(
ID INT IDENTITY PRIMARY KEY
,DocumentId INT
,Xml XML
)
CREATE PRIMARY XML INDEX PXML_Table_Xml
ON #Table (Xml);
GO
INSERT INTO #Table
(
DocumentId
,Xml
)
VALUES
(
1
,
'
<root>
<node search="0"><id>10088</id><text></text></node>
<node search="0"><id>10087</id><text></text></node>
<node search="0"><id>10090</id><text></text></node>
</root>
'
)
DECLARE #DesiredCategories TABLE(DocumentId INT,CategoryID INT, Search BIT, SearchText NVARCHAR(50));
INSERT INTO #DesiredCategories
SELECT
DocumentId
,CategoryID
,Search
,SearchText
FROM #Table
CROSS APPLY
(
SELECT
X.Col.query('id').value('.', 'INT') as CategoryID,
X.Col.value('#search', 'BIT') as Search,
X.Col.query('text').value('.', 'NVARCHAR(MAX)') as SearchText
FROM Xml.nodes('root/node') X(Col)
) A
SELECT * FROM #DesiredCategories