PATCH: Add DTrace probes

[Paul van den Bogaard]

OK, By heart, not tested!


/*
	To check how well we are allocating connections from memory instead  
of creating them.
	Of course a connection is merely a piece of memory and not a  
resource intense thing as
	a database connection. But stil.
*/
memcached*:::conn-allocate
{
	@["allocated"] = count();
}
memcached*:::conn-create
{
	@["created"] = count();
}

/*
	The above can be combined like:

	Must say I have never seen the comma separator while
	only specifying the probename.
*/

memcached*:::conn-allocate,
memcached*:::conn-create
{
	@[probename] =count();
}

/*
	How many system calls were there, and which one
	between allocation of a connection and the release
	of it.
*/

memcached*:::conn-allocate
{
	self->allocate = arg0;
}

memcached*:::conn-release
/self->allocate/
{
	self->allocate = 0;		/* Not sure if 0 is a valid value for a connID  
though. If that's the case this does not work */	
}

syscall:::entry
/self->allocate/
{
	@syscalls[pid, probefunc] = count();
}


it is basically this way of using a combination of multiple  
providers  that makes DTrace unique. If you use internal stats  
counters they just provide a story without context.

Have fun playing with it. Questions? Ask. Sometime I now an anwer ;^)

--Paul


On 7-mrt-2008, at 15:42, Roy Lyseng wrote:

> Well, I hoped it would spur some more clever ideas...
>
> I thought it could be useful if you have some problems with your  
> application, and can use dtrace to track what operations are  
> actually performed on one particular key.
>
> But aggregations may probably be more interesting.
>
> Roy
>
> Paul van den Bogaard wrote:
>> Mmm, I think that if copyinstr(arg1) == '1234..." that your trace  
>> output will be rather dull :-)
>> --Paul
>> On 7-mrt-2008, at 14:37, Roy Lyseng wrote:
>>> Another, slightly more advanced script is memcached-keytrace.d:
>>>
>>> :memcached::command-set,command-add,command-delete,command-get
>>> /pid == $target && copyinstr(arg1) == "123456789"/
>>> {
>>>     trace(copyinstr(arg1));
>>> }
>>>
>>> END
>>> {
>>> }
>>>
>>> This one will trace set, add, delete and get commands applied to  
>>> one specific key:
>>>
>>> Invoke as:
>>>
>>> dtrace -s ~/memcached/dtrace/memcached-trace.d -p 24167
>>>
>>> Then run a telnet session:
>>>
>>> telnet system 11211
>>> Trying 9.9.9.9...
>>> Connected to system.
>>> Escape character is '^]'.
>>> abcdefghij
>>> ERROR
>>> set 123456789 0 0 10
>>> abcdefghij
>>> STORED
>>> delete 123456789 0 0
>>> DELETED
>>> get 123456789 0 0 0
>>> END
>>>
>>> And the dtrace script reports:
>>>
>>> CPU     ID                    FUNCTION:NAME
>>>   1  54165       complete_nread:command-set   123456789
>>>   0  54159 process_delete_command:command-delete   123456789
>>>   1  54160  process_get_command:command-get   123456789
>>>
>>> Useful? Maybe...
>>>
>>> Roy
>>> Dustin Sallings wrote:
>>>>   For those of us who haven't truly unleashed the power of  
>>>> dtrace, can you describe the kinds of things we can learn from  
>>>> this (perhaps with scripts)?
>>>> --Dustin Sallings (mobile)
>>>> On Mar 6, 2008, at 4:48, Trond Norbye <Trond.Norbye at Sun.COM> wrote:
>>>>>
>>>>> On Mar 5, 2008, at 3:52 PM, Trond Norbye wrote:
>>>>>
>>>>>> The following patch adds a new configure-option (--enable- 
>>>>>> dtrace) that adds DTrace probes to various parts of memcached.
>>>>>>
>>>>>> Please comment.
>>>>>>
>>>>>> Trond
>>>>>
>>>>> I discovered that I had some "leftovers" in this patch from  
>>>>> before I fixed the comments regarding the large page support..
>>>>>
>>>>> The attached version is replacement for the original patch.
>>>>>
>>>>> Trond
>>>>> <dtrace.patch.gz>
>>>>>
>> --------------------------------------------------------------------- 
>> ------------------------ Paul van den  
>> Bogaard                               Paul.vandenBogaard at sun.com
>> ISV-E  -- ISV Engineering, Opensource Engineering group
>> Sun Microsystems, Inc                              phone:         
>> +31 334 515 918
>> Saturnus 1                                                  
>> extentsion: x (70)15918
>> 3824 ME Amersfoort                                 mobile:        
>> +31 651 913 354
>> The Netherlands                                         
>> fax:            +31 334 515 001

------------------------------------------------------------------------ 
---------------------
Paul van den Bogaard                                
Paul.vandenBogaard at sun.com
ISV-E  -- ISV Engineering, Opensource Engineering group

Sun Microsystems, Inc                              phone:        +31  
334 515 918
Saturnus 1                                                  
extentsion: x (70)15918
3824 ME Amersfoort                                 mobile:       +31  
651 913 354
The Netherlands                                         
fax:            +31 334 515 001