new memcached slab display/tuning tool

[Brad Fitzpatrick]

It's Friday, so here's something fun for y'all:

I finally wrote that script I talk about a lot to show and tune your slab
page usage in memcached.

There's no automatic mode yet, because I can't decide the heuristics to
use, but I'll let you smart people decide that for yourself, and send me
patches perhaps.  :-)

First off, the script is both in cvs and at:

     http://www.danga.com/memcached/dist/memcached-tool

Here's a demo of it in action on one of LiveJournal's memcached processes:

lj@grimace:~$ memcached-tool
Usage: memcached-tool <host[:port]> [mode]

       memcached-tool 10.0.0.5:11211 display    # shows slabs
       memcached-tool 10.0.0.5:11211            # same.  (default is display)
       memcached-tool 10.0.0.5:11211 move 7 9   # takes 1MB slab from class #7
                                                # to class #9.

You can only move slabs around once memory is totally allocated, and only
once the target class is full.  (So you can't move from #6 to #9 and #7
to #9 at the same itme, since you'd have to wait for #9 to fill from
the first reassigned page)



lj@grimace:~$ memcached-tool 10.0.0.41:11211
  # Item_Size  Max_age  1MB_pages Full?
  6      64 B  12869 s      82     yes
  7     128 B  12446 s      74     yes
  8     256 B  11069 s      91     yes
  9     512 B  12184 s      54     yes
 10      1 kB  12120 s     106     yes
 11      2 kB  11498 s     181     yes
 12      4 kB  10087 s     189     yes
 13      8 kB   8322 s     124     yes
 14     16 kB   7335 s      69     yes
 15     32 kB   4591 s      31     yes
 16     64 kB   3378 s      17     yes
 17    128 kB  39944 s       6     yes


lj@grimace:~$ memcached-tool 10.0.0.41:11211 move 17 16
Success.


lj@grimace:~$ memcached-tool 10.0.0.41:11211 move 17 16
Error: can't move from 17 to 16.  Destination not yet full?  See usage docs.


lj@grimace:~$ memcached-tool 10.0.0.41:11211
  # Item_Size  Max_age  1MB_pages Full?
  6      64 B  12687 s      82     yes
  7     128 B  12338 s      74     yes
  8     256 B  10968 s      91     yes
  9     512 B  11950 s      54     yes
 10      1 kB  11931 s     106     yes
 11      2 kB  11421 s     181     yes
 12      4 kB   9986 s     189     yes
 13      8 kB   8356 s     124     yes
 14     16 kB   7240 s      69     yes
 15     32 kB   4584 s      31     yes
 16     64 kB   3257 s      18      no
 17    128 kB  40287 s       5     yes


Enjoy!  Have a nice weekend!

- Brad