How to extract SQL from SQL Server XML Deadlock Graphs - sql-server

Question

I have some SQL deadlocks I am trying to capture mediaName from. The deadlock report is in XML but the attribute i need is buried in XML, then SQL, then XML again. Here is an example.
XPATH for where the SQL starts is /deadlock/process-list/process/inputbuf, then the SQL is:
SET DEADLOCK_PRIORITY 8;
EXEC spM_Ext_InsertUpdateXML N'<mediaRecords><media
title="This Is the title" mediaType="0"
creationTime="2018-03-16T00:59:43" origSOM="01:00:00;00" notes="Air Date:
2018-03-18 &#xa;Air Window: 3 &#xa;" mediaName="This is what i need"
><mediaInstances><mediaInstance directory="here"
duration="00:28:40;11" version="1" position="00:00:00;00" mediaSetId="34"
creationStartTime="2018-03-16T00:59:43;25" creationEndTime="2018-03-
16T00:59:43;25"/></mediaInstances><properties><
classifications><classification category="HD" classification="Content
Resolution"/></classifications><markups><markup
name=""><Item duration="00:00:10;00" orderNo="1"
type="Dynamic" som="00:59:50;00" comment=""
name="Segment"/></markup><markup
name="Segment"><markupItem duration="00:08:41;10" orderNo="2"
type="Dynamic" som="01:00:00;00" comment="Main Title and Segment 1 |
ID:SEDC" name="Segment"/></markup><markup
name="Black"><markup
See how the XML isnt using < and > for the elements but the &lt and &gt which adds complexity.
I am trying to extract only mediaName from this report but cant get past the above mentioned XPath with powershell. Was hoping someone might have an idea. I was using
$xml = [xml](Get-Content "C:\Users\user\desktop\test.xml")
$xml.SelectNodes('/deadlock/process-list/process/inputbuf') | select mediaName
I have also tried piping select-xml to where-object but I don't think I am using the right $_.[input]
With the help of tomalak and the answer below this is the fixed and working parsing script.
#report file location, edited by user when needed
$DeadlockReport = "C:\Users\User\Desktop\xml_report1.xml"
# Create object to load the XML from the deadlock report and find the SQL within
$xml = New-Object xml
$xml.Load($DeadlockReport)
$inputbuf = $xml.SelectNodes('//deadlock/process-list/process/inputbuf')
$value = $inputbuf.'#text'
#find the internal XML and replace bad values, SQL, and truncation with RE
$value = $value -replace "^[\s\S]*?N'","" -replace "';\s*$","" -replace "<markup.*$","</properties></media></mediaRecords>"
#append root elements to $value
$fix = "<root>" + $value + "</root>"
#Load the XML after its been corrected
$payload.LoadXml($fix)
#find the nodes in the xml for mediaName
$mediaName = $payload.SelectNodes('//root/mediaRecords/media/#mediaName')
#iterate through and return all media names.
foreach($i in $mediaName)
{
return $mediaName
}

Answer 1

What you have is:
an XML file,
which contains a string value,
which is SQL,
which contains another string value,
which is XML again.
So let's peel the onion.
First-off, please never load XML files like this
# this is bad code, don't use
$xml = [xml](Get-Content "C:\Users\user\desktop\test.xml")
XML has sophisticated file encoding detection, and you are short-circuiting that by letting Powershell load the file. This can lead to data breaking silently because Powershell's Get-Content has no idea what actual encoding of the XML file is. (Sometimes the above works, sometimes it doesn't. "It works for me" doesn't mean that you're doing it right, it means that you're being lucky.)
This is the correct way:
$xml = New-Object xml
$xml.Load("C:\Users\user\desktop\test.xml")
Here the XmlDocument object will take care of loading the file and transparently adapt to any encoding it might have. Nothing can break and you don't have to worry about file encodings.
Second, don't let the looks of the XML file in a text editor deceive you. As indicated, /deadlock/process-list/process/inputbuf contains a string as far as XML is concerned, the < and > and all the rest will be there when you look at the actual text value of the element.
$inputbuf = $xml.SelectSingleNode('/deadlock/process-list/process/inputbuf')
$value = $inputbuf.'#text'
Write-Host $value
Would print something like this, which is SQL:
SET DEADLOCK_PRIORITY 8;
EXEC spM_Ext_InsertUpdateXML N'<mediaRecords><media
title="This Is the title" mediaType="0"
creationTime="2018-03-16T00:59:43" origSOM="01:00:00;00" notes="Air Date:
2018-03-18
Air Window: 3
" mediaName="This is what i need"
><mediaInstances><mediaInstance directory="here"
duration="00:28:40;11" version="1" position="00:00:00;00" mediaSetId="34"
creationStartTime="2018-03-16T00:59:43;25" creationEndTime="2018-03-
16T00:59:43;25"/></mediaInstances><properties><
classifications><classification category="HD" classification="Content
Resolution"/></classifications><markups><markup
name=""><Item duration="00:00:10;00" orderNo="1"
type="Dynamic" som="00:59:50;00" comment=""
name="Segment"/></markup><markup
name="Segment"><markupItem duration="00:08:41;10" orderNo="2"
type="Dynamic" som="01:00:00;00" comment="Main Title and Segment 1 |
ID:SEDC" name="Segment"/></markup><markup
name="Black"><markup ...
</mediaRecords>';
And the XML you are interested in is actually a string inside this SQL. If the SQL follows this pattern...
SET DEADLOCK_PRIORITY 8;
EXEC spM_Ext_InsertUpdateXML N'<...>';
...we need to do three things in order to get to the XML payload:
Remove the enclosing SQL statements
Replace any '' with ' (because the '' is the escaped quote in SQL strings)
Pray that part in-between does not contain any other SQL expressions
So
$value = $value -replace "^[\s\S]*?N'","" -replace "';\s*$","" -replace "''","'"
would remove everything up to and including N' and the '; at the end, as well as replace all the duplicated single quotes (if any) with normal single quotes.
Adapt the regular expressions as needed. Replacing the SQL parts with regex isn't exactly clean, but if the expected input is very limited, like in this case, it'll do.
Write-Host $value
Now we should have a string that is actually XML. Let's parse it. This time, it's already in our memory, there isn't any file encoding to pay attention to. So it's actually all-right if we cast it to XML directly:
$payload = [xml]$value
And now we can query it for the value you are interested in:
$mediaName = $payload.SelectSingleNode("/mediaRecords/media/#mediaName")
Write-Host $mediaName