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WinDBG Walkthrough - Dump Values Of DataSet or DataTable

WinDBG Walkthrough - Dump Values Of DataSet or DataTable

  • Comments 4
 Alik Levin    This walkthrough is completely based on Johan's post WinDBG+SOS: Getting at the values in a DataTable. I have created this one to help me do the job in straightforward way next time I hit similar problem. Joan also offers few scripts for process automation - recommended.

image 
by glennharper

Customer Case Study

The customer complained about potential memory leak. Following the procedure described in Identifying Memory Leak With Process Explorer And Windbg we realized that we are dealing with static variable that grows in unlimited way. This assumption is based on the fact that after running !gcroot on the leaking type we get the following:

HANDLE(Strong):23b1cd0:Root:0x12571730.....

After reviewing Tess' .NET Debugging Demos Lab 7: Memory Leak - Review we found the following which made us believe we are dealing with static variable:

DOMAIN(001CCE68):HANDLE(Strong) - Strong reference, Typically a static variable

To identify what this static variable is we needed to dump its values. The variable was a DataTable. I have not found a straightforward way of dumping contents of DataTable. This is the walkthrough that does the job.

Summary of steps

  • Step 1. Dump DataTables
  • Step 2. Dump DataTable
  • Step 3. Dump columnCollection
  • Step 4. Dump list object
  • Step 5. Dump raw memory - dd command
  • Step 6. Dump DataColumn
  • Step 7. Dump storage
  • Step 8. Dump values
  • Step 9. Bonus - automation

Step 1. Dump DataTables

The objective of this step is identify all DataTable object and pick the one of the interest

0:000> !dumpdatatables
DataTable       Rows    Columns    DataSet nextRowID ColumnCount
-----------------------------------------------------------------------------------------------
0x024dc948 0x024dcbc8 0x024dcdec 0x064f2400         1         2
0x025156b8 0x02515938 0x02515b5c 0x02515478         1         7
...

0x0e5b9ce4 0x0e5b9f64 0x0e5ba138 0x0e55a338       428         5
0x06510e54 0x065110d4 0x065112a8 0x064f2400     1,359         7
0x0e5778f0 0x0e577b70 0x0e577d44 0x0e55a338     1,359         7
0x0a55d270 0x0a55d4f0 0x0a55d6c4 0x06a62620 4,194,305        10
Total 61 DataTable objects

Step 2. Dump DataTable

The objective of this step is identifying the address of columnCollection of the DataTable.

0:000> !do 0x0a55d270
Name: System.Data.DataTable
...
0x176c1560 0x40003f2     0x18                CLASS   instance 0x0a55d6c4 columnCollection
...

Step 3. Dump columnCollection

The objective of this step is identifying  the address of list object of the columnCollection.

0:000> !do 0x0a55d6c4
Name: System.Data.DataColumnCollection
...
0x176c5ffc 0x4000377      0x8                CLASS   instance 0x0a55d6f8 list
...

Step 4. Dump list object

The objective of this step is identifying the address of _items object.

0:000> !do 0x0a55d6f8
Name: System.Collections.ArrayList
...
0x79ba75ec 0x4000362      0x4                CLASS   instance 0x0a55d710 _items
...

Step 5. Dump raw memory - dd command

The objective of this step is identifying addresses of DataColumn objects.

0:000> dd 0x0a55d710
0a55d710  01e5209c 00000010 79b92eec 0a55d854
0a55d720  0a55d8d4 0a55d954 0a55d9d4 0a55da54
0a55d730  0a55dad4 0a55db54 0a55dbd4 0a55dd74

Step 6. Dump DataColumn

The objective of this step is identifying the address of storage object.

!do 0a55d854
Name: System.Data.DataColumn
...
0x176c69e8 0x400036b     0x48                CLASS   instance 0x0a55df40 storage
...

Step 7. Dump storage

The objective of this step is identifying address of value object.

0:000> !do 0x0a55df40
Name: System.Data.Common.Int32Storage
...
0x176ecc8c 0x4000729     0x10                CLASS   instance 0x4dbd0030 values
...

Step 8. Dump values

The objective of this step is dumping the actual values, finally...

0:000> !do 0x4dbd0030
Name: System.Int32[]
...
Content: 8,388,608 items

Ouch, it is array.... !do -v will dump its values, but I am afraid it is not a good idea doing it for 8 million items here ;)

Step 9. Bonus - automation

The objective of this step is automate the process of dumping values (Step 8):

  • Create a text file named dumparray and save it in WinDBG directory. The contents of the file are:
    • .foreach ( o { !do ${$arg1} -v -short }) { !do ${o} }
  • Run the following command in WinDBG to dump the values of the array
    • $$>a< dumparray 0x4dbd0030

Related Materials

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  • !dumpdatatables isn't available with SOS.dll for .net 2.0 externally as yet. I guess we need to do a

    !dumpheap -type System.Data.DataTable

    to get started

  • Good catch AtulGupta!

    Thanks for calling this out.

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