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Optimize XML XML Server Performance

I have 34 rows in the database, each row contains a column containing xml - xml is actually in the NVARCHAR (MAX) column, and not in the XML column.

For each row, I select the values ​​in the xml elements as one set of results. Performance is pretty bad. I tried two different queries. The first takes about 22 seconds, and the second takes 7.

Even at 7 seconds it is much slower than optimal, I hope for 1-2 seconds.

So, I read a rumor on the Internet that if you convert NVARCHAR data to XML using a temp table or table, you will achieve a performance gain, which, at least in my case, was true ... Now it runs in under the second. Now I am looking for explanations that can explain to me why these 2 approaches really affect performance.

22 seconds:

SELECT
    c.ID,
    c.ChannelName,
    [Name] = d.c.value('name[1]','varchar(100)'),
    [Type] = d.c.value('transportName[1]','varchar(100)'),
    [Enabled] = d.c.value('enabled[1]','BIT'),
    [Queued] = d.c.value('properties[1]/destinationConnectorProperties[1]/queueEnabled[1]','varchar(100)'),
    [RetryInterval] = d.c.value('properties[1]/destinationConnectorProperties[1]/retryIntervalMillis[1]','INT'),
    [MaxRetries] = d.c.value('properties[1]/destinationConnectorProperties[1]/retryCount[1]','INT'),
    [RotateQueue] = d.c.value('properties[1]/destinationConnectorProperties[1]/rotate[1]','BIT'),
    [ThreadCount] = d.c.value('properties[1]/destinationConnectorProperties[1]/threadCount[1]','INT'),
    [WaitForPrevious] = d.c.value('waitForPrevious[1]','BIT'),
    [Destination] = COALESCE(
        d.c.value('properties[1]/channelId[1]','varchar(100)'),
        d.c.value('properties[1]/remoteAddress[1]','varchar(100)'),
        d.c.value('properties[1]/wsdlUrl[1]','varchar(1024)')),

    [DestinationPort] = COALESCE(
        d.c.value('properties[1]/remotePort[1]','varchar(100)'),
        d.c.value('properties[1]/port[1]','varchar(1024)')),
    [Service] = d.c.value('properties[1]/service[1]','varchar(1024)'),
    [Operation] = d.c.value('properties[1]/operation[1]','varchar(1024)')
FROM
(
    SELECT
            [ID],
            [ChannelName] = [Name],
            [CFG] = Convert(XML, Channel)
    FROM
            dbo.CHANNEL
) c
CROSS APPLY c.CFG.nodes('/channel/destinationConnectors/connector') d(c)

7 seconds, due to the use of text (). I do not know why the text speeds up the work.

SELECT
    c.ID,
    c.ChannelName,
    [Name] = d.c.value('(name/text())[1]','varchar(100)'),
    [Type] = d.c.value('(transportName/text())[1]','varchar(100)'),
    [Enabled] = d.c.value('(enabled/text())[1]','BIT'),
    [Queued] = d.c.value('(properties/destinationConnectorProperties/queueEnabled/text())[1]','varchar(100)'),
    [RetryInterval] = d.c.value('(properties/destinationConnectorProperties/retryIntervalMillis/text())[1]','INT'),
    [MaxRetries] = d.c.value('(properties/destinationConnectorProperties/retryCount/text())[1]','INT'),
    [RotateQueue] = d.c.value('(properties/destinationConnectorProperties/rotate/text())[1]','BIT'),
    [ThreadCount] = d.c.value('(properties/destinationConnectorProperties/threadCount/text())[1]','INT'),
    [WaitForPrevious] = d.c.value('(waitForPrevious/text())[1]','BIT'),
    [Destination] = COALESCE(
        d.c.value('(properties/channelId/text())[1]','varchar(100)'),
        d.c.value('(properties/remoteAddress/text())[1]','varchar(100)'),
        d.c.value('(properties/wsdlUrl/text())[1]','varchar(1024)')),

    [DestinationPort] = COALESCE(
        d.c.value('(properties/remotePort/text())[1]','varchar(100)'),
        d.c.value('(properties/port/text())[1]','varchar(1024)')),
    [Service] = d.c.value('(properties/service/text())[1]','varchar(1024)'),
    [Operation] = d.c.value('(properties/operation/text())[1]','varchar(1024)')
FROM
(
    SELECT
            [ID],
            [ChannelName] = [Name],
            [CFG] = Convert(XML, Channel)
    FROM
            dbo.CHANNEL
) c
CROSS APPLY c.CFG.nodes('/channel/destinationConnectors/connector') d(c)

This query uses the text () method, but first it converts the NVARCHAR column to the xml column in the table variable. Running in less than a second ...

DECLARE @Xml AS TABLE (
    [ID] NVARCHAR(36) NOT NULL Primary Key,
    [Name] NVARCHAR(100) NOT NULL,
    [CFG] XML NOT NULL
);

INSERT INTO @Xml (ID, Name, CFG)
SELECT
    c.ID,
    c.Name,
    Convert(XML, c.Channel)
FROM
    [dbo].[CHANNEL] c;

SELECT
    c.ID,
    c.ChannelName,
    [Name] = d.c.value('(name/text())[1]','varchar(100)'),
    [Type] = d.c.value('(transportName/text())[1]','varchar(100)'),
    [Enabled] = d.c.value('(enabled/text())[1]','BIT'),
    [Queued] = d.c.value('(properties/destinationConnectorProperties/queueEnabled/text())[1]','varchar(100)'),
    [RetryInterval] = d.c.value('(properties/destinationConnectorProperties/retryIntervalMillis/text())[1]','INT'),
    [MaxRetries] = d.c.value('(properties/destinationConnectorProperties/retryCount/text())[1]','INT'),
    [RotateQueue] = d.c.value('(properties/destinationConnectorProperties/rotate/text())[1]','BIT'),
    [ThreadCount] = d.c.value('(properties/destinationConnectorProperties/threadCount/text())[1]','INT'),
    [WaitForPrevious] = d.c.value('(waitForPrevious/text())[1]','BIT'),
    [Destination] = COALESCE(
        d.c.value('(properties/channelId/text())[1]','varchar(100)'),
        d.c.value('(properties/remoteAddress/text())[1]','varchar(100)'),
        d.c.value('(properties/wsdlUrl/text())[1]','varchar(1024)')),

    [DestinationPort] = COALESCE(
        d.c.value('(properties/remotePort/text())[1]','varchar(100)'),
        d.c.value('(properties/port/text())[1]','varchar(1024)')),
    [Service] = d.c.value('(properties/service/text())[1]','varchar(1024)'),
    [Operation] = d.c.value('(properties/operation/text())[1]','varchar(1024)')
FROM
(
    SELECT
            [ID],
            [ChannelName] = [Name],
            [CFG]
    FROM
            @Xml
) c
CROSS APPLY c.CFG.nodes('/channel/destinationConnectors/connector') d(c)
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1 answer

I can give you one answer and one guess:

:

DECLARE @tbl TABLE(s NVARCHAR(MAX));
INSERT INTO @tbl VALUES
(N'<root>
    <SomeElement>This is first text of element1
        <InnerElement>This is text of inner element1</InnerElement>
        This is second text of element1
    </SomeElement>
    <SomeElement>This is first text of element2
        <InnerElement>This is text of inner element2</InnerElement>
        This is second text of element2
    </SomeElement>
</root>')
,(N'<root>
    <SomeElement>This is first text of elementA
        <InnerElement>This is text of inner elementA</InnerElement>
        This is second text of elementA
    </SomeElement>
    <SomeElement>This is first text of elementB
        <InnerElement>This is text of inner elementB</InnerElement>
        This is second text of elementB
    </SomeElement>
</root>');

- XML . CTE, ...

SELECT se.value(N'(.)[1]','nvarchar(max)') SomeElementsContent
      ,se.value(N'(InnerElement)[1]','nvarchar(max)') InnerElementsContent
      ,se.value(N'(./text())[1]','nvarchar(max)') ElementsFirstText
      ,se.value(N'(./text())[2]','nvarchar(max)') ElementsSecondText
FROM (SELECT CAST(s AS XML) FROM @tbl) AS tbl(TheXml)
CROSS APPLY TheXml.nodes(N'/root/SomeElement') AS A(se);

- XML :

DECLARE @tbl2 TABLE(x XML)
INSERT INTO @tbl2
SELECT CAST(s AS XML) FROM @tbl;

SELECT se.value(N'(.)[1]','nvarchar(max)') SomeElementsContent
      ,se.value(N'(InnerElement)[1]','nvarchar(max)') InnerElementsContent
      ,se.value(N'(./text())[1]','nvarchar(max)') ElementsFirstText
      ,se.value(N'(./text())[2]','nvarchar(max)') ElementsSecondText
FROM @tbl2 t2
CROSS APPLY t2.x.nodes(N'/root/SomeElement') AS A(se);

/text() , /text()?

, - , node node. text() - . . text() - ( ). . , - , text().

XML ?

XML - ! . XML , . XML . , , XML, XML, . XML ( ), (re) .

...
() . SQL Server , . , , , !. , , , . !
. CONVERT ( CAST) - . , , , , ...

+1

Source: https://habr.com/ru/post/1690369/

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