Debugging Script: Dumping out ASP.NET Session Contents
In my last post I wrote a script to dump out all the ASP.NET requests on the heap. Since one of the most common memory issues I encounter is too much cache or session state I figured that showing you how to retrieve session data would be good.
A word of caution, since this script uses !dumpheap (to dump out the objects on the heap) and !objsize (to figure out the size of an object including the size of its member variables) it may take a long time to execute if you have a very large dump, which is typically the case when you are worried about how much you store in session state.
There is a lot more data that you can get, other than what I am displaying, and the script can pretty easily be modified to display cache objects instead so if you find some cool use or modification of it, please post it in the comments so all of us can benefit from it.
Note: This script only works if you use in-proc session state since it is doing its magic by dumping out all the System.Web.SessionState.InProcSessionState items on the heap. On the other hand, if you have high memory usage due to session state it is probably the in-proc session state items you will be worried about. Btw, if this is what you are running into, check out the post index for other posts on ASP.NET Session memory issues.
Output and comments on output
This script is divided into two parts.
DumpSessions
Displays all the System.Web.SessionState.InProcSessionState items with the session address as a DML (Debugger Markup Language) link so that you can click it to get more detailed info.
DumpSessionVar
Dumps out more detailed information about each sessions, i.e. the session variables for that particular session and this is what gets executed when you click the DML link.
An idea for a modification of the script would be to print out all the session variables at once, or add some parsing to get the total size of all sessions. Oh well, there is endless possibilities here.
Finding the data
All in-proc sessions are represented on the heap as System.Web.SessionState.InProcSessionState objects.
0:013> !do 03093d38
Name: System.Web.SessionState.InProcSessionState
MethodTable: 663ac580
EEClass: 663ac510
Size: 48(0x30) bytes
GC Generation: 1
(C:\WINDOWS\assembly\GAC_32\System.Web\2.0.0.0__b03f5f7f11d50a3a\System.Web.dll)
Fields:
MT Field Offset Type VT Attr Value Name
663ecfbc 4001edc 4 ...ateItemCollection 0 instance 03093b18 _sessionItems
663a3390 4001edd 8 ...ObjectsCollection 0 instance 00000000 _staticObjects
791018e0 4001ede c System.Int32 1 instance 20 _timeout
79107584 4001edf 18 System.Boolean 1 instance 0 _locked
791084f8 4001ee0 1c System.DateTime 1 instance 03093d54 _utcLockDate
791018e0 4001ee1 10 System.Int32 1 instance 1 _lockCookie
663aad40 4001ee2 24 ...ReadWriteSpinLock 1 instance 03093d5c _spinLock
791018e0 4001ee3 14 System.Int32 1 instance 0 _flags
given a particular System.Web.SessionState.InProcSessionState object we can get to the information we want like this.
Size of the session
0:013> !objsize 03093d38
sizeof(03093d38) = 268,437,272 ( 0x10000718) bytes (System.Web.SessionState.InProcSessionState)
Individual Session Variables
We get to the individual session variables by dumping out the _sessionItems member variable, following the steps below…
Note: the number of session variables in the session is available from the _size member variable of the ArrayList
0:013> !do 03093b18
Name: System.Web.SessionState.SessionStateItemCollection
MethodTable: 66411bb4
EEClass: 66411b3c
Size: 60(0x3c) bytes
GC Generation: 2
(C:\WINDOWS\assembly\GAC_32\System.Web\2.0.0.0__b03f5f7f11d50a3a\System.Web.dll)
Fields:
MT Field Offset Type VT Attr Value Name
79107584 4001173 24 System.Boolean 1 instance 0 _readOnly
79105cd4 4001174 4 ...ections.ArrayList 0 instance 03093b60 _entriesArray
791138d4 4001175 8 ...IEqualityComparer 0 instance 03049ce0 _keyComparer
79101634 4001176 c ...ections.Hashtable 0 instance 03093b78 _entriesTable
7a761668 4001177 10 ...e+NameObjectEntry 0 instance 00000000 _nullKeyEntry
7a78e3b0 4001178 14 ...se+KeysCollection 0 instance 00000000 _keys
7910ec98 4001179 18 ...SerializationInfo 0 instance 00000000 _serializationInfo
791018e0 400117a 20 System.Int32 1 instance 4 _version
790fc35c 400117b 1c System.Object 0 instance 00000000 _syncRoot
79115538 400117c 538 ...em.StringComparer 0 shared static defaultComparer
>> Domain:Value 0019b498:NotInit 001cc780:NotInit <<
79107584 4001f2b 25 System.Boolean 1 instance 1 _dirty
664228fc 4001f2c 28 ...n+KeyedCollection 0 instance 00000000 _serializedItems
79100f74 4001f2d 2c System.IO.Stream 0 instance 00000000 _stream
791018e0 4001f2e 34 System.Int32 1 instance 0 _iLastOffset
790fc35c 4001f2f 30 System.Object 0 instance 03093b54 _serializedItemsLock
79101634 4001f2a c54 ...ections.Hashtable 0 shared static s_immutableTypes
>> Domain:Value 0019b498:NotInit 001cc780:0708be1c <<
0:013> !do 03093b60
Name: System.Collections.ArrayList
MethodTable: 79105cd4
EEClass: 79105c28
Size: 24(0x18) bytes
GC Generation: 2
(C:\WINDOWS\assembly\GAC_32\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll)
Fields:
MT Field Offset Type VT Attr Value Name
7912ad90 40008df 4 System.Object[] 0 instance 03093c90 _items
791018e0 40008e0 c System.Int32 1 instance 3 _size
791018e0 40008e1 10 System.Int32 1 instance 3 _version
790fc35c 40008e2 8 System.Object 0 instance 00000000 _syncRoot
7912ad90 40008e3 1c0 System.Object[] 0 shared static emptyArray
>> Domain:Value 0019b498:03031ff8 001cc780:030371e4 <<
0:013> dc 03093c90
03093c90 7912ad90 00000004 790fc35c 03093c80 ...y....\..y.<..
03093ca0 03093cb0 03093ce4 00000000 00000000 .<...<..........
03093cb0 7a761668 030939c8 03093c64 00000000 h.vz.9..d<......
03093cc0 79105cd4 31180038 00000000 020bb7a8 .\.y8..1........
03093cd0 020bb7a8 00000000 00194d40 00000000 ........@M......
03093ce0 00000000 7a761668 03093a14 03093cc0 ....h.vz.:...<..
03093cf0 00000000 790fcb30 0000001a 00000019 ....0..y........
03093d00 0061006a 006e0030 00710078 007a006e j.a.0.n.x.q.n.z.
0:013> !do 03093c80
Name: System.Collections.Specialized.NameObjectCollectionBase+NameObjectEntry
MethodTable: 7a761668
EEClass: 7a7ce36c
Size: 16(0x10) bytes
GC Generation: 2
(C:\WINDOWS\assembly\GAC_MSIL\System\2.0.0.0__b77a5c561934e089\System.dll)
Fields:
MT Field Offset Type VT Attr Value Name
790fcb30 400117d 4 System.String 0 instance 030939a4 Key
790fc35c 400117e 8 System.Object 0 instance 03093c40 Value
0:013> !do 030939a4
Name: System.String
MethodTable: 790fcb30
EEClass: 790fca90
Size: 34(0x22) bytes
GC Generation: 2
(C:\WINDOWS\assembly\GAC_32\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll)
String: UserName
Fields:
MT Field Offset Type VT Attr Value Name
791018e0 4000096 4 System.Int32 1 instance 9 m_arrayLength
791018e0 4000097 8 System.Int32 1 instance 8 m_stringLength
790fe534 4000098 c System.Char 1 instance 55 m_firstChar
790fcb30 4000099 10 System.String 0 shared static Empty
>> Domain:Value 0019b498:790d81bc 001cc780:790d81bc <<
7912b1d8 400009a 14 System.Char[] 0 shared static WhitespaceChars
>> Domain:Value 0019b498:030303f4 001cc780:03034558 <<
0:013> !do 03093c40
Name: System.String
MethodTable: 790fcb30
EEClass: 790fca90
Size: 36(0x24) bytes
GC Generation: 2
(C:\WINDOWS\assembly\GAC_32\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll)
String: Joe Smith
Fields:
MT Field Offset Type VT Attr Value Name
791018e0 4000096 4 System.Int32 1 instance 10 m_arrayLength
791018e0 4000097 8 System.Int32 1 instance 9 m_stringLength
790fe534 4000098 c System.Char 1 instance 4a m_firstChar
790fcb30 4000099 10 System.String 0 shared static Empty
>> Domain:Value 0019b498:790d81bc 001cc780:790d81bc <<
7912b1d8 400009a 14 System.Char[] 0 shared static WhitespaceChars
>> Domain:Value 0019b498:030303f4 001cc780:03034558 <<
Running the scripts
To run the scripts copy the text below and put it in two text files somewhere on your hard drive.
I’ve put mine in c:\tools\extensions\DumpSessions.wds and c:\tools\extensions\DumpSessionVar.wds.
If you put them somewhere else, make sure you change the path in the DumpSessions.wds script so that you get to the right script file when you click the DML links.
To run it, open up your dump in windbg and load sos.dll, and then run
$><c:\tools\extensions\DumpSessions.wdl
Script code
DumpSessions.wds
$$
$$ Dumps all sessions on the heap
$$
$$
$$ Written by: Tess
$$
$$ Run as: $><c:\tools\extensions\DumpSessions.wds
$$
$$ CLEAR ALL ALIASES (VARIABLES)
$$ ----------------------------------------------------------------------------------
ad /q *
r @$t0=0;
r @$t1=0;
$$ GET ALL SESSION ITEMS
.foreach (CurrentSession {!dumpheap -type System.Web.SessionState.InProcSessionState -short}){
$$ Increment # of sessions
r @$t0 = @$t0+1
.printf /D "Session Address:\t<?dml?><exec cmd=\"$$>a< c:\\tools\\extensions\\DumpSessionVar.wds ${CurrentSession}\">${CurrentSession}</exec>\n";
.printf "Session Timeout:\t%d\n", poi(${CurrentSession}+0xc);
.foreach /pS 2 /ps 99 (token {!objsize ${CurrentSession}}){.printf "Session Size:\t${token} bytes\n"}
.printf "_______________________________________________\n";
}
.printf "Number of Sessions: %d\n\n\n\n\n\n\n\n\n", @$t0;
DumpSessionVar.wds
$$
$$ Dumps details of a particular session
$$
$$
$$ Written by: Tess
$$
$$ Run as: $$>a<c:\tools\extensions\DumpSessionVar.wds SessionAddress
$$
.printf "Session:\t\t${$arg1}\n";
.foreach /pS 2 /ps 99 (token {!objsize ${$arg1}}){.printf "Session Size:\t${token} bytes\n"}
$$ Number of session variables
r @$t0 = poi(poi(poi(${$arg1}+0x4)+0x4)+0xc);
.for(r @$t1=0; @$t1 < @$t0; r @$t1=@$t1+1){
.printf "\n================================================\n"
.printf "Session Variable\n"
.printf "================================================\n"
$$ NameObject Entry (actual session variable)
r @$t2 = poi(poi(poi(poi(${$arg1}+0x4)+0x4)+0x4)+0x8+0x4*(@$t1+1));
$$ Size
.foreach /pS 2 /ps 99 (token {!objsize @$t2}){.printf "Sessionvar Size:\t${token} bytes\n"}
$$ Key
.foreach /pS 5 (tk {.foreach /pS 9 (token {!do -nofields poi(@$t2+0x4)}){.printf "${token} "}}) {
.printf /D "Session Key:\t<?dml?><col fg=\"emphfg\">${tk}</col>\n"
};
$$ Value
.printf "Session Variable:\t%p\n****\n", poi(@$t2+0x8);
!do poi(@$t2+0x8)
}
.printf "\n\n\n\n\n\n\n\n\n";
ad /q *
Final words
You can access all the scripts from this blog in the debugging scripts repo
If you have any ideas for scripts that you think would be useful please let me know and if I have the time and energy I will probably implement and post them…
Have fun,
Tess
