PATCH: Add DTrace probes

[Trond Norbye]

On Mar 6, 2008, at 5:27 PM, 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)?
>

The following script will monitor the hash-table and dump out the "top  
ten" requested keys and the distribution in of the "search-depth"  
every 10 seconds:

#! /usr/bin/ksh
pid=`pgrep -x memcached`
if [ -z "${pid}" ]
then
    echo memcached not running
    exit 1
fi

file /proc/${pid}/path/a.out | grep "ELF 64" > /dev/zero 2>&1
if [ $? -ne 0 ]
then
   mode="-32"
else
   mode="-64"
fi

/usr/sbin/dtrace ${mode} -n '
#pragma D option quiet

memcached'${pid}':::assoc-find
{
     @assK[copyinstr(arg0)] = count();
     @assD = quantize(arg1);
}

tick-10s
{
     printf("Top 10 keys\n");
     trunc(@assK, 10);
     printa(@assK);
     trunc(@assK, 0);

     printf("assoc-find depth\n");
     printa(@assD);
     clear(@assD);
}

END {
     trunc(@assK, 10);
     printa(@assK);
     trunc(@assK, 0);

     printf("assoc-find depth\n");
     printa(@assD);
     clear(@assD);
}
'