Tools Tips and Tricks #10: Caching PDB files locally


When you are debugging a SQL Server memory dump, you would need the PDB files associated with the sqlservr.exe that you are debugging to get the call stacks. The PDB files can be downloaded from the Microsoft Symbol Server. Paul Randal [Blog | Twitter] in a previous blog post showed how to do this using symchk.exe. If you want to download symbols for multiple EXEs then you either need to create a script file or you could use the method mentioned below provided you have a dump file that you are interested in.

Today I am going to explain how to download PDB files using CDB (Command Line Debugger) and command script file. The first ingredient for this is a memory dump file (.mdmp or .dmp). Once you have the dump and the Windows Debugging Tools installed on your local machine, you use the following command to cache the symbols to a local folder:

C:\Program Files\Debugging Tools for Windows (x64)>cdb -y srv*D:\PublicSymbols*http://msdl.microsoft.com/download/symbols -z “D:\SQLDump0134.mdmp” -cfr “D:\ExecuteSymbolFetch.txt” > D:\DebuggingExample.txt

The –y parameter specifies the local folder into which the symbols need to be cached and the –z parameter is the path to the memory dump file. The –cfr parameter takes the path to the script file which contains the script file to be executed. The contents of my script file are:

!sym noisy
.reload /f
lmvm sqlservr
qd

When you look into the DebuggingExample.txt file once the download has completed, you will find the output of the lmvm command which will show you that the PDB file was cached locally:

0:031> lmvm sqlservr
sqlservr   (pdb symbols)          d:\publicsymbols\sqlservr.pdb\389EF554D94A4947846D85FCDC4233382\sqlservr.pdb

Alternatively, you could load the dump using WinDBG and then using the commands from the script file mentioned above to cache the symbols. You would need to set the symbol file path using File->Symbol File Path or CTRL+S option or using the debugger command .sympath. Once that is done, you can executed .reload /f to download the PDB files from the Microsoft Symbol Server. This is helpful when you need symbol files while capturing certain debugging diagnostic data like generating the XML file with the callstacks from a Process Monitor trace as shown here or if you want to perform an analysis using the existing scripts provided with the Debug Diagnostic tool.

Debugging Download location:
64-bit Debugging Tools
32-bit Debugging Tools

References:
Using Script files for Windows Debugger
Command line CDB options

Tools, Debugging, Tools Tips and Tricks

Tools Tips and Tricks #9: PSSDIAG Configuration Manager


I had been waiting for Diag Manager to be made public so that this post could go online. Diag Manager is a configuration tool that is used by CSS Engineers to configure a consolidated data collection for Windows Perfmon counters and SQL Server profiler trace (server-side). Additionally, the tool lets you add pre-configured custom diagnostics for Analysis Services configuration data, Mirroring configuration, Event log collection etc. and even custom data collection (using .sql scripts/custom utilities) which can be added using the Custom Diagnostics-> _MyCollectors option. (UI Screenshot below)

image

The tip that I want to talk about with this tool is that .CAB file generated uses a PSSDIAG.XML configuration file when using SQLDIAG to collect data. If you need to collect data from multiple different instances using the same configuration file, then you can just use the same extracted .CAB file contents with small tweaks to the SQLDIAG.XML file.

Changing the machine name from which the data needs to be collected: Change the machine name to the appropriate machine name.

<Machine name="MyLaptop">

Changing the instance name from which the data needs to be collected: Change the instance name value to the appropriate SQL Server instance name. MSSQLSERVER as instance name for default instance.

<Instance name="INST1" windowsauth="true" ssver="10" user="">

Disabling/Enabling perfmon data collection: Change the enabled option to true to enable perfmon data collection or false to disable collection. The maxfilesize parameter controls the perfmon file rollover size.

<PerfmonCollector enabled="true" pollinginterval="5" maxfilesize="256">

Changing the profiler trace collection and the rollover file size: Change the enabled value to true/false to enable/disable profiler data collection. Changing the maxfilesize parameter value controls the rollover file size for the profiler traces.

<ProfilerCollector enabled="true" template="_GeneralPerformance90.xml" pollinginterval="5" maxfilesize="350">

Collecting SQLDIAG output during startup/shutdown: This can be controlled using the enabled parameter value and the startup parameter value determines if the SQLDIAG output is to be collected during PSSDIAG startup/initialization. The shutdown parameter controls whether a SQLDIAG output needs to be captured once PSSDIAG collection is signaled to be stopped using CTRL+C.

<SqldiagCollector enabled="true" startup="false" shutdown="true" />

The other option that you have now that you have a GUI is to using Diag Manager to configure a new package for your target machine and click on Save. You will notice in the Save Configuration window, you have two locations that can be modified, one for the PSSDIAG.XML file and one for the .CAB file. Generate a new PSSDIAG.XML file and replace the existing file from a previously configured PSSDIAG with the newly generated PSSDIAG.XML for your new settings to take effect when the PSSDIAG launched again.

Another option that engineers use regularly for a long term PSSDIAG collection is the “Delete Old Trace Files” custom diagnostics. This is an option that is used for long term data collection. More information about this custom diagnostic is available in the FAQs section on Codeplex.

Note: The XML configuration for SQL Server 2008 and 2008 R2 can be mixed and matched using the ssver=”10.5” for SQL Server 2008 R2 instances and ssver=”10” for SQL Server 2008 instances. However, you shouldn’t use the same configured package across different platforms (x86/x64/ia64) and nor should you use the same package for different releases of SQL Server (2005/2008/2008 R2).

We have also documented some Common Issues faced while collecting data using a configured package. In case you have a question regarding the tool, feel free to post a new discussion. In case you find a defect that you need to report, you can log the defect under the Issue Tracker section.

Blog post talking about the release: http://blogs.msdn.com/b/psssql/archive/2011/05/24/pssdiag-sqldiag-configuration-manager-released-to-codeplex.aspx

This is a widely used tool in Microsoft Services for consolidated data collection while working on SQL Server performance issues. In case you have any feedback, please feel free to provide the same on the discussion forum for the tool on Codeplex.

Tools Tips and Tricks #8 – Debug Diagnostic and Crash Rules


Screenshot 1There are multiple instances where you might need to collect a dump for a process which generates an Access Violation or just setup a crash rule for an application that crashes and that doesn’t generate a dump to investigate further. So today I am going to imagedemonstrate a way to capture a crash dump of a process using the Debug Diagnostic Tool. The example shown here can be extended to SQL Server as well. Once you launch the Debug Diagnostic Tool, you will notice that the tool has 3 different tabs namely Rule, Advanced Analysis and Processes.

I am now going to walkthrough setting up of a Crash Rule for an EXE called DebugDiag_CrashRule.exe which I had written to generate an Access Violation and then no exception handler written in the code which would result in a termination of the EXE.

The steps that you can use to setup the Crash Rule are:

1. Use the Rule tab and click on the Add Rule button. Select the option “Crash” in the Select Rule Type window and click on Next. (see screenshot on the left)
2. Then select “A specific process” option in the Select Target Type window and click on Next. (see screenshot on the right)
3. Next you are presented with an option to select a process from the list of active processes. imageI gave the process name in the Selected Processes text-box and didn’t select the “This process instance only” option. If you select this option, then the monitoring will be setup for only the particular instance that you have selected. If left unchecked, then the monitoring will be setup for any instance of the process spawned on the machine. (see screenshot on the right). Click on Next after you have given the appropriate process name or selected the process ID.
4. In the next screen “Advanced Configuration”, I clicked on the Exceptions button which lets you configure actions for First Chance Exceptions for the process being monitored. Click on the Add Exception button on the First Chance Exception Configuration window. Select Access Violation for the exception name and for the Action Type, select Full User Dump. The Action Limit that I have set in this case is 6 which means that after 6 dumps captured by this rule, no further dumps will be generated. This is a good way of limiting the number of dumps that will be generated for the process that you are monitoring. Notice that that Action type for unconfigured first chance exceptions is set to None. This means that for any first chance exception that is generated apart from the one that you have configured, no action will be taken by the rule. (see screenshot below).

imageimageimage

5. Next you get the “Select Dump Location and Rule Name” window where you can changed the rule name and the location of the dumps generation. By default the dumps are generated at <Debug Diagnostic Install Path>\Logs\<Rule Name> folder. (see screenshot on the left)
6. In the last window, use the Activate option to enable the rule.

Now that the rule is active, when I launch my EXE, I can find that the Being Debugged column has the value “Yes” for DebugDiag_CrashRule.exe under the Processes tabs. I launched my application once and this generated 2 dumps. The Rules tab will show you the rule configured, status of the rule and the number of dumps captured by the rule and the location of the dump. (see screenshot above)

Now that the data is captured, the tool allows you to perform Crash Analysis using the Advanced Analysis tab. Using the Analyze Data button, you can analyze the dump files together and get a HTML report of the dumps captured. The Analysis of the dumps generated should be done on a non-production machine to prevent an overhead of downloading symbols and performing the analysis. The symbol search path can be provided using the Tools –> Options and Settings –> Folders and Search Path tab. The symbol search path would be: SRV*<local folder>*http://msdl.microsoft.com/download/symbols. A local folder is always good to have so that the symbols used are cached locally if required later. This prevents having to connect to the Microsoft Symbol Server everytime you analyze a dump.

This is what I see in the DebugDiag_CrashRule__PID__3576__Date__05_24_2011__Time_12_59_56AM__612__First Chance Access Violation.dmp file. It tells me that Thread 0 generated the dump. As you can see in the screenshot below, the report gives you the call stack as well. The Exception information shows that an Access Violation was raised while trying to write to a memory location by a sprintf function called by the DebugDiag_CrashRule EXE.

Exception Information

In DebugDiag_CrashRule__PID__6476__Date__05_24_2011__Time_12_08_12AM__341__First Chance Access Violation.dmp the assembly instruction at msvcr100!vcwprintf_s+2f07 in C:\Windows\System32\msvcr100.dll from Microsoft Corporation has caused an access violation exception (0xC0000005) when trying to write to memory location 0x3f9721d0 on thread 0

image

The HTML report has a similar output for the DebugDiag_CrashRule__PID__3576__Date__05_24_2011__Time_12_59_57AM__647__Second_Chance_Exception_C0000005.dmp file as well. An additional file DebugDiag_CrashRule__PID__3576__Date__05_24_2011__Time_12_59_56AM__612__ProcessList.txt is also generated which contains a list of processes running on the machine when the dump was generated. All the reports are saved in the <Debug Diagnostic install path>\Reports folder by default.

Hope this makes it easier to capture crash dumps for processes which are terminating without giving you much information in the Windows event logs or the logs generated by the application. This is a tool that is commonly used by CSS to configure crash rules on a machine and capture crash dumps.

Once you have collected the required data, you can go to the Rules tab, right click on the rule and click on De-activate rule. Once the rule status shows up as Not Active, you can choose to remove the rule by right-clicking on the rule and selecting the Remove Rule option.

The Debug Diagnostic Tool v1.1 available on the Microsoft Downloads site doesn’t have a x64 version which lets you configure rules and monitor processes for Windows Server 2008/R2/Windows 7/Windows Vista. The 64-bit version of the tool only has Advanced Analysis option. The Debug Diagnostic Tool v1.2 available from here has a 64-bit download (Beta version) which allows to configure rules and monitor processes for Windows Server 2008/R2/Windows 7/Windows Vista.

TIP: Let’s talk about a quick tip about taking dumps of a SQL Server process using Debug Diagnostic tool. In case you find that your SQL Server process is hung and you cannot log into the SQL instance using Dedicated Administrator Connection (DAC) or don’t have DAC enabled for the instance, then you can take a mini-dump using the Processes tab.

Steps
1. Click on the Processes tab.
2. Right-click on the process name sqlservr.exe. If you have multiple instances, you can identify the correct instance using the Active Services column which will give you the instance name. (see screenshot below)
3. Right-click on the process name, click on Create Full Userdump or Create Mini Userdump option to generate a full or mini memory dump of the selected process. The dump location will be default location configured for the dump under Tools –> Options and Settings –> Folders and Search Path tab –> Manual Userdump Save Folder. By default it is <Debug Diagnostic install path>\Logs\Misc.image

imageYou might also encounter a situation where you are required to take a dump of a process every n seconds/minutes. This can be done by right clicking on the process name and selecting the Create Userdump series… option. This will give you a window with the set of options as seen in the screenshot on the left. As you can see, it lets you configure a number of options for the process namely:

1. Time interval between each dump created
2. When to start the timer, before or after the dump file writing completes.
3. When to stop generating the dumps
4. Whether to collect Full or Mini dumps
5. Option to collect a single Full user dump when a Mini-dump series is created for a process before or after the series is completed.

Tess Ferrandez [Blog], an Escalation Engineer in CSS, also has a pretty detailed blog post on how to setup a crash rule for ASP.NET applications.

Note: For a 64-bit process (eg. 64-bit SQL Server instance) which has a large process address space, it would be advisable to configure a User Mini Dump as the Exception action instead of a full-user dump. When a dump file is generated, the process threads are frozen to take a snapshot. For a large dump generation on a system with a slow Disk IO, you might end up with SQL outages and on a cluster it can result in a failover during the dump generation period.