Debugging Ruby

DEBUGGING RUBY
Aman Gupta
@tmm1
AS RUBYISTS, WE'VE SEEN...
nasty bugs
ejpphoto (flickr)
fatboyke (flickr)
code
memory bloat
37prime (flickr)
THIS TALK IS ABOUT...
TOOLS TO FIX THESE ISSUES.

TOOLS FOR LINUX.
lsof
strace
ltrace
pleeker (flickr)
TOOLS FOR C CODE.
perftools
gdb
booddin (flickr)
TOOLS FOR NETWORKS.
tcpdump
ngrep
pascal.charest (flickr)
TOOLS FOR CPU USAGE.
perftools
perftools.rb
marksze (flickr)
TOOLS FOR MEMORY USAGE.
bleak_house
gdb.rb
kgrocki (flickr) memprof
IGNORE THE FINE PRINT
mayu (flickr) delgrossodotcom (flickr)

LSOF
list open files
lsof -nPp <pid>

lsof -nPp <pid>
-n
Inhibits the conversion of network numbers to host names.
-P
Inhibits the conversion of port numbers to names for network files
FD TYPE NAME json

cwd DIR /var/www/myapp memcached
txt REG /usr/bin/ruby mysql
mem REG /json-1.1.9/ext/json/ext/generator.so http
mem REG /json-1.1.9/ext/json/ext/parser.so
mem REG /memcached-0.17.4/lib/rlibmemcached.so
mem REG /mysql-2.8.1/lib/mysql_api.so
0u CHR /dev/null
1w REG /usr/local/nginx/logs/error.log
2w REG /usr/local/nginx/logs/error.log
3u IPv4 10.8.85.66:33326->10.8.85.68:3306 (ESTABLISHED)
12u REG /tmp/RackMultipart.28957.0
STRACE
trace system calls and signals
strace -cp <pid>

strace -ttTp <pid> -o <file>
strace -cp <pid>
-c
Count time, calls, and errors for each system call and report a
summary on program exit.
-p pid
Attach to the process with the process ID pid and begin tracing.
% time seconds usecs/call calls errors syscall

------ ----------- ----------- --------- --------- ----------------
50.39 0.000064 0 1197 592 read
34.65 0.000044 0 609 writev
14.96 0.000019 0 1226 epoll_ctl
0.00 0.000000 0 4 close
0.00 0.000000 0 1 select
0.00 0.000000 0 4 socket
0.00 0.000000 0 4 4 connect
0.00 0.000000 0 1057 epoll_wait
------ ----------- ----------- --------- --------- ----------------
100.00 0.000127 4134 596 total
strace -ttTp <pid> -o <file>
-t
Prefix each line of the trace with the time of day.
-tt
If given twice, the time printed will include the microseconds.
-T
Show the time spent in system calls.
-o filename
Write the trace output to the file filename rather than to stderr.
epoll_wait(9, {{EPOLLIN, {u32=68841296, u64=68841296}}}, 4096, 50) = 1 <0.033109>

accept(10, {sin_port=38313, sin_addr="127.0.0.1"}, [1226]) = 22 <0.000014>
fcntl(22, F_GETFL) = 0x2 (flags O_RDWR) <0.000007>
fcntl(22, F_SETFL, O_RDWR|O_NONBLOCK) = 0 <0.000008>
setsockopt(22, SOL_TCP, TCP_NODELAY, [1], 4) = 0 <0.000008>
accept(10, 0x7fff5d9c07d0, [1226]) = -1 EAGAIN <0.000014>
epoll_ctl(9, EPOLL_CTL_ADD, 22, {EPOLLIN, {u32=108750368, u64=108750368}}) = 0 <0.000009>
epoll_wait(9, {{EPOLLIN, {u32=108750368, u64=108750368}}}, 4096, 50) = 1 <0.000007>
read(22, "GET / HTTP/1.1\r"..., 16384) = 772 <0.000012>
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0 <0.000007>
poll([{fd=5, events=POLLIN|POLLPRI}], 1, 0) = 0 (Timeout) <0.000008>
write(5, "1\0\0\0\0\0\0-\0\0\0\3SELECT * FROM `table`"..., 56) = 56 <0.000023>
read(5, "\25\1\0\1,\2\0x\234m"..., 16384) = 284 <1.300897>
http client connection
read 772 bytes
read(22, "GET / HTTP/1.1\r"..., 16384) = 772 <0.0012>
incoming http request

took 0.0012s
mysql connection
write sql query to db
write(5, "SELECT * FROM `table`"..., 56) = 56 <0.0023>

read(5, "\25\1\0\1,\2\0x\234m"..., 16384) = 284 <1.30>
read query
response
slow query
stracing ruby: SIGVTALRM
--- SIGVTALRM (Virtual timer expired) @ 0 (0) ---
rt_sigreturn(0x1a) = 2207807 <0.000009>
rt_sigreturn(0x1a) = 0 <0.000009>
rt_sigreturn(0x1a) = 140734552062624 <0.000009>
rt_sigreturn(0x1a) = 140734552066688 <0.000009>
rt_sigreturn(0x1a) = 11333952 <0.000008>
rt_sigreturn(0x1a) = 0 <0.000009>
rt_sigreturn(0x1a) = 1 <0.000010>
• ruby 1.8 uses signals to schedule its green threads

• process receives a SIGVTALRM signal every 10ms
stracing ruby: sigprocmask
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
100.00 0.326334 0 3568567 rt_sigprocmask
0.00 0.000000 0 9 read
0.00 0.000000 0 10 open
0.00 0.000000 0 10 close
0.00 0.000000 0 9 fstat
0.00 0.000000 0 25 mmap
------ ----------- ----------- --------- --------- ----------------
100.00 0.326334 3568685 0 total
• debian/redhat compile ruby with --enable-pthread

• uses a native thread timer for SIGVTALRM
• causes excessive calls to sigprocmask: 30% slowdown!
TCPDUMP
dump traffic on a network
tcpdump -i eth0 -s 0 -nqA

tcp dst port 3306
tcpdump -i <eth> -s <len> -nqA <expr>
tcpdump -i <eth> -w <file> <expr>
-i <eth>
Network interface.
-s <len>
Snarf len bytes of data from each packet.
-n
Don't convert addresses (host addresses, port numbers) to names.
-q
Quiet output. Print less protocol information.
-A
Print each packet (minus its link level header) in ASCII.
-w <file>
Write the raw packets to file rather than printing them out.
<expr>
libpcap expression, for example:
tcp src port 80
tcp dst port 3306
tcp dst port 80
19:52:20.216294 IP 24.203.197.27.40105 >
174.37.48.236.80: tcp 438
E...*.@.l.%&.....%0....POx..%s.oP.......
GET /poll_images/cld99erh0/logo.png HTTP/1.1
Accept: */*
Referer: http://apps.facebook.com/realpolls/?
_fb_q=1
tcp dst port 3306
19:51:06.501632 IP 10.8.85.66.50443 >
10.8.85.68.3306: tcp 98
E..."K@.@.Yy
.UB
.UD.....z....L............
GZ.y3b..[......W....
SELECT * FROM `votes` WHERE (`poll_id` =
72621) LIMIT 1
tcpdump -w <file>
PERFTOOLS
google's cpu profiler
CPUPROFILE=/tmp/myprof ./myapp
pprof ./myapp /tmp/myprof
wget http://google-perftools.googlecode.com/files/google-
perftools-1.6.tar.gz download
tar zxvf google-perftools-1.6.tar.gz
cd google-perftools-1.6
./configure --prefix=/opt
make compile
sudo make install
# for linux
export LD_PRELOAD=/opt/lib/libprofiler.so setup
# for osx
export DYLD_INSERT_LIBRARIES=/opt/lib/libprofiler.dylib
CPUPROFILE=/tmp/ruby.prof ruby -e' profile

5_000_000.times{ "hello world" }
'
pprof `which ruby` --text /tmp/ruby.prof report

pprof ruby pprof ruby
ruby.prof --text ruby.prof --gif
Total: 103 samples
95 92.2% rb_yield_0
103 100.0% rb_eval
12 11.7% gc_sweep
52 50.5% rb_str_new3
3 2.9% obj_free
103 100.0% int_dotimes
12 11.7% gc_mark
Profiling MRI
• 10% of production
VM time spent in
rb_str_sub_bang
• String#sub!
• called from
Time.parse
return unless str.sub!(/\A(\d{1,2})/, '')

return unless str.sub!(/\A( \d|\d{1,2})/, '')
return unless str.sub!(/\A( \d|\d{1,2})/, '')
Profiling EM + threads
Total: 3763 samples
2764 73.5% catch_timer
989 26.3% memcpy
3 0.1% st_lookup
2 0.1% rb_thread_schedule
1 0.0% rb_eval
1 0.0% rb_newobj
1 0.0% rb_gc_force_recycle
• known issue: EM+threads =

slow
• memcpy??
• thread context switches copy
the stack w/ memcpy
• EM allocates huge buffer on
the stack
• solution: move buffer to the
heap
PERFTOOLS.RB
perftools for ruby code
pprof.rb /tmp/myrbprof
github.com/tmm1/perftools.rb
gem install perftools.rb
RUBYOPT="-r`gem which perftools | tail -1`"

CPUPROFILE=/tmp/myrbprof
ruby myapp.rb
pprof.rb /tmp/myrbprof --text

pprof.rb /tmp/myrbprof --gif > /tmp/myrbprof.gif
require 'sinatra'
$ ab -c 1 -n 50 http://127.0.0.1:4567/compute
$ ab -c 1 -n 50 http://127.0.0.1:4567/sleep
get '/sleep' do
sleep 0.25
'done' • Sampling profiler:
end
• 232 samples total
get '/compute' do • 83 samples were in /compute
proc{ |n|
a,b=0,1 • 118 samples had /compute on
the stack but were in
n.times{ a,b = b,a+b } another function
b
}.call(10_000) • /compute accounts for 50%
'done' of process, but only 35% of
time was in /compute itself
end
== Sinatra has ended his set (crowd applauds)

PROFILE: interrupts/evictions/bytes = 232/0/2152
Total: 232 samples

83 35.8% 35.8% 118 50.9% Sinatra::Application#GET /compute
56 24.1% 59.9% 56 24.1% garbage_collector
35 15.1% 75.0% 113 48.7% Integer#times
CPUPROFILE_REALTIME=1
CPUPROFILE=app.prof
CPUPROFILE=app-rt.prof
redis-rb bottleneck
why is rubygems slow?
faster
bundle
install
• 23% spent in
Gem::Version#<=>
• simple patch to rubygems
improved overall install
performance by 15%
• http://gist.github.com/
458185
CPUPROFILE_OBJECTS=1
CPUPROFILE=app-objs.prof
• object allocation profiler

mode built-in
• 1 sample = 1 object
created
• Time parsing is both
CPU and object
allocation intensive
• using mysql2 moves
this to C
LTRACE
trace library calls
ltrace -cp <pid>

ltrace -ttTp <pid> -o <file>
ltrace -c ruby threaded_em.rb
% time seconds usecs/call calls function
------ ----------- ----------- --------- --------------------
48.65 11.741295 617 19009 memcpy
30.16 7.279634 831 8751 longjmp
9.78 2.359889 135 17357 _setjmp
8.91 2.150565 285 7540 malloc
1.10 0.265946 20 13021 memset
0.81 0.195272 19 10105 __ctype_b_loc
0.35 0.084575 19 4361 strcmp
0.19 0.046163 19 2377 strlen
0.03 0.006272 23 265 realloc
------ ----------- ----------- --------- --------------------
100.00 24.134999 82999 total
ltrace -c ruby threaded_em.rb
% time seconds usecs/call calls function
------ ----------- ----------- --------- --------------------
48.65 11.741295 617 19009 memcpy
30.16 7.279634 831 8751 longjmp
9.78 2.359889 135 17357 _setjmp
8.91 2.150565 285 7540 malloc
1.10 0.265946 20 13021 memset
0.81 0.195272 19 10105 __ctype_b_loc
0.35 0.084575 19 4361 strcmp
0.19 0.046163 19 2377 strlen
0.03 0.006272 23 265 realloc
------ ----------- ----------- --------- --------------------
100.00 24.134999 82999 total
ltrace -ttT -e memcpy ruby threaded_em.rb

01:24:48.769408 --- SIGVTALRM (Virtual timer expired) ---
01:24:48.769616 memcpy(0x1216000, "", 1086328) = 0x1216000 <0.000578>
01:24:48.770555 memcpy(0x6e32670, "\240&\343v", 1086328) = 0x6e32670 <0.000418>
01:24:49.899414 --- SIGVTALRM (Virtual timer expired) ---

01:24:49.899490 memcpy(0x1320000, "", 1082584) = 0x1320000 <0.000628>
01:24:49.900474 memcpy(0x6e32670, "", 1086328) = 0x6e32670 <0.000479>
LTRACE/LIBDL
trace dlopen’d library calls
ltrace -F <conf> -bg -x

<symbol> -p <pid>
github.com/ice799/ltrace/tree/libdl
ltrace -F <conf> -b -g -x <sym>
-b
Ignore signals.
-g
Ignore libraries linked at compile time.
-F <conf>
Read prototypes from config file.
-x <sym>
Trace calls to the function sym.
-s <num>
Show first num bytes of string args.
-F ltrace.conf
int mysql_real_query(addr,string,ulong);
void garbage_collect(void);
int memcached_set(addr,string,ulong,string,ulong);
ltrace -x garbage_collect
19:08:06.436926 garbage_collect() = <void> <0.221679>
ltrace -x mysql_real_query
mysql_real_query(0x1c9e0500, "SET NAMES 'UTF8'", 16) = 0 <0.000324>
mysql_real_query(0x1c9e0500, "SET SQL_AUTO_IS_NULL=0", 22) = 0 <0.000322>
mysql_real_query(0x19c7a500, "SELECT * FROM `users`", 21) = 0 <1.206506>
mysql_real_query(0x1c9e0500, "COMMIT", 6) = 0 <0.000181>
ltrace -x memcached_set
memcached_set(0x15d46b80, "Status:33", 21, "\004\b", 366) = 0 <0.01116>
GDB
the GNU debugger
gdb <executable>
gdb attach <pid>
Debugging Ruby Segfaults
test_segv.rb:4: [BUG] Segmentation fault
ruby 1.8.7 (2008-08-11 patchlevel 72) [i686-darwin9.7.0]
#include "ruby.h"
VALUE
segv()
{
VALUE array[1];
array[1000000] = NULL;
return Qnil;
}
void
Init_segv()
{
rb_define_method(rb_cObject, "segv", segv, 0);
}
Debugging Ruby Segfaults
test_segv.rb:4: [BUG] Segmentation fault
ruby 1.8.7 (2008-08-11 patchlevel 72) [i686-darwin9.7.0]
def test
#include "ruby.h" require 'segv'
4.times do
VALUE Dir.chdir '/tmp' do
segv() Hash.new{ segv }[0]
{ end
VALUE array[1]; end
array[1000000] = NULL; end
return Qnil;
} sleep 10
test()
void
Init_segv()
{
rb_define_method(rb_cObject, "segv", segv, 0);
}
1. Attach to running process
$ ps aux | grep ruby
joe 23611 0.0 0.1 25424 7540 S Dec01 0:00 ruby test_segv.rb
$ sudo gdb ruby 23611

Attaching to program: ruby, process 23611
0x00007fa5113c0c93 in nanosleep () from /lib/libc.so.6
(gdb) c
Continuing.
Program received signal SIGBUS, Bus error.

segv () at segv.c:7
7 array[1000000] = NULL;
1. Attach to running process
$ ps aux | grep ruby
joe 23611 0.0 0.1 25424 7540 S Dec01 0:00 ruby test_segv.rb
$ sudo gdb ruby 23611

Attaching to program: ruby, process 23611
0x00007fa5113c0c93 in nanosleep () from /lib/libc.so.6
(gdb) c
Continuing.
Program received signal SIGBUS, Bus error.

segv () at segv.c:7
7 array[1000000] = NULL;
2. Use a coredump
Process.setrlimit Process::RLIMIT_CORE, 300*1024*1024
$ sudo mkdir /cores
$ sudo chmod 777 /cores
$ sudo sysctl kernel.core_pattern=/cores/%e.core.%s.%p.%t
$ sudo gdb ruby /cores/ruby.core.6.23611.1259781224

def test
require 'segv'
4.times do
Dir.chdir '/tmp' do
Hash.new{ segv }[0]
end
end (gdb) where
end #0 segv () at segv.c:7
#1 0x000000000041f2be in call_cfunc () at eval.c:5727
test() ...
#13 0x000000000043ba8c in rb_hash_default () at hash.c:521
...
#19 0x000000000043b92a in rb_hash_aref () at hash.c:429
...
#26 0x00000000004bb7bc in chdir_yield () at dir.c:728
#27 0x000000000041d8d7 in rb_ensure () at eval.c:5528
#28 0x00000000004bb93a in dir_s_chdir () at dir.c:816
...
#35 0x000000000041c444 in rb_yield () at eval.c:5142
#36 0x0000000000450690 in int_dotimes () at numeric.c:2834
...
#48 0x0000000000412a90 in ruby_run () at eval.c:1678
#49 0x000000000041014e in main () at main.c:48
GDB.RB
gdb with MRI hooks
gem install gdb.rb

gdb.rb <pid>
github.com/tmm1/gdb.rb
(gdb) ruby eval 1+2
3
(gdb) ruby eval Thread.current

#<Thread:0x1d630 run>
(gdb) ruby eval Thread.list.size

8
(gdb) ruby threads list
0x15890 main thread THREAD_STOPPED WAIT_JOIN(0x19ef4)
0x19ef4 thread THREAD_STOPPED WAIT_TIME(57.10s)
0x19e34 thread THREAD_STOPPED WAIT_FD(5)
0x19dc4 thread THREAD_STOPPED WAIT_NONE
0x19dc8 thread THREAD_STOPPED WAIT_NONE
0x19dcc thread THREAD_STOPPED WAIT_NONE
0x22668 thread THREAD_STOPPED WAIT_NONE
0x1d630 curr thread THREAD_RUNNABLE WAIT_NONE
(gdb) ruby objects
HEAPS 8
SLOTS 1686252
LIVE 893327 (52.98%)
FREE 792925 (47.02%)
scope 1641 (0.18%)

regexp 2255 (0.25%)
data 3539 (0.40%)
class 3680 (0.41%)
hash 6196 (0.69%)
object 8785 (0.98%)
array 13850 (1.55%)
string 105350 (11.79%)
node 742346 (83.10%)
(gdb) ruby objects strings
140 u'lib'
158 u'0'
294 u'\n'
619 u''
30503 unique strings

3187435 bytes
def test
require 'segv'
4.times do
Dir.chdir '/tmp' do
Hash.new{ segv }[0]
end
end
end
(gdb) ruby threads
test()
0xa3e000 main curr thread THREAD_RUNNABLE WAIT_NONE
node_vcall segv in test_segv.rb:5
node_call test in test_segv.rb:5
node_call call in test_segv.rb:5
node_call default in test_segv.rb:5
node_call [] in test_segv.rb:5
node_call chdir in test_segv.rb:4
node_call times in test_segv.rb:3
node_vcall test in test_segv.rb:9
rails_warden leak
(gdb) ruby objects classes
1197 MIME::Type
2657 NewRelic::MetricSpec
2719 TZInfo::TimezoneTransitionInfo
4124 Warden::Manager
4124 MethodOverrideForAll
4124 AccountMiddleware
4124 Rack::Cookies
4125 ActiveRecord::ConnectionAdapters::ConnectionManagement
4125 ActionController::Session::CookieStore
4125 ActionController::Failsafe
4125 ActionController::ParamsParser
4125 Rack::Lock
4125 ActionController::Dispatcher
4125 ActiveRecord::QueryCache
4125 ActiveSupport::MessageVerifier
4125 Rack::Head
middleware chain leaking per request

mongrel sleeper thread
0x16814c00 thread THREAD_STOPPED WAIT_TIME(0.47) 1522 bytes
node_fcall sleep in lib/mongrel/configurator.rb:285
node_fcall run in lib/mongrel/configurator.rb:285
node_fcall loop in lib/mongrel/configurator.rb:285
node_call run in lib/mongrel/configurator.rb:285
node_call initialize in lib/mongrel/configurator.rb:285
node_call new in lib/mongrel/configurator.rb:285
node_call run in bin/mongrel_rails:128
node_call run in lib/mongrel/command.rb:212
node_call run in bin/mongrel_rails:281
node_fcall (unknown) in bin/mongrel_rails:19
def run
@listeners.each {|name,s|
s.run
}
$mongrel_sleeper_thread = Thread.new { loop { sleep 1 } }

end
god memory leaks
(gdb) ruby objects arrays 43 God::Process
elements instances 43 God::Watch
94310 3 43 God::Driver
94311 3 43 God::DriverEventQueue
94314 2 43 God::Conditions::MemoryUsage
94316 1 43 God::Conditions::ProcessRunning
43 God::Behaviors::CleanPidFile
5369 arrays 45 Process::Status
2863364 member elements 86 God::Metric
327 God::System::SlashProcPoller
many arrays with 327 God::System::Process
90k+ elements! 406 God::DriverEvent
5 separate god leaks fixed by Eric

Lindvall with the help of gdb.rb!
ruby method cache
(gdb) ruby methodcache
Module#extend wipes the UnboundMethod#arity
Hash#[]=
entire method cache! Class#private
Array#freeze
(gdb) b rb_clear_cache Module#Integer
Breakpoint 1 at 0x41067b: file eval.c, line 351. Fixnum#<
(gdb) c Class#is_a?
Continuing. Fixnum#+
Class#protected
Breakpoint 1, rb_clear_cache () at eval.c:351 Class#>=
351 if (!ruby_running) return;
2028 empty slots (99.02%)
(gdb) ruby threads
0x1623000 main curr thread THREAD_RUNNABLE WAIT_NONE
node_call extend_object in sin.rb:23
node_call extend in sin.rb:23
node_call GET /other in lib/sinatra/base.rb:779
node_call GET /other in lib/sinatra/base.rb:779
node_call call in lib/sinatra/base.rb:779
node_fcall route in lib/sinatra/base.rb:474
BLEAK_HOUSE
ruby memory leak detector
ruby-bleak-house myapp.rb
bleak /tmp/bleak.<PID>.*.dump
github.com/fauna/bleak_house
• BleakHouse
• installs a patched version of ruby: ruby-bleak-house
• unlike gdb.rb, see where objects were created
(file:line)
• create multiple dumps over time with `kill -USR2
<pid>` and compare to find leaks
191691 total objects

Final heap size 191691 filled, 220961 free
Displaying top 20 most common line/class pairs
89513 __null__:__null__:__node__
41438 __null__:__null__:String
2348 ruby/site_ruby/1.8/rubygems/specification.rb:557:Array
1508 ruby/gems/1.8/specifications/gettext-1.9.gemspec:14:String
1021 ruby/gems/1.8/specifications/heel-0.2.0.gemspec:14:String
951 ruby/site_ruby/1.8/rubygems/version.rb:111:String
935 ruby/site_ruby/1.8/rubygems/specification.rb:557:String
834 ruby/site_ruby/1.8/rubygems/version.rb:146:Array
MEMPROF
a heap visualizer for ruby
gem install memprof

open http://memprof.com
github.com/ice799/memprof
memprof.com
http://www.scribd.com/doc/31772032/memprof
plugging a leak in rails3
• in dev mode, rails3 is leaking 10mb per request
plugging a leak in rails3
• in dev mode, rails3 is leaking 10mb per request
let’s use memprof to find it!
# in environment.rb
require `gem which memprof/signal`.strip
plugging a leak
in rails3
send the app some
requests so it leaks
$ ab -c 1 -n 30
http://localhost:3000/
tell memprof to dump

out the entire heap to
json
$ memprof
--pid <pid>
--name <dump name>
--key <api key>
plugging a leak
in rails3
send the app some
requests so it leaks
$ ab -c 1 -n 30
http://localhost:3000/
tell memprof to dump

out the entire heap to
json
$ memprof
--pid <pid>
--name <dump name>
--key <api key>
2519 classes
2519 classes
30 copies of
TestController
2519 classes
30 copies of
TestController
mongo query for all

TestController classes
2519 classes
30 copies of
TestController
mongo query for all

TestController classes
details for one copy of

TestController
find references to object
holding references
to all controllers
“leak” is on line 178
holding references
to all controllers
• In development mode, Rails reloads all your
application code on every request
• ActionView::Partials::PartialRenderer is caching
partials used by each controller as an optimization
• But.. it ends up holding a reference to every single
reloaded version of those controllers
• In development mode, Rails reloads all your
application code on every request
• ActionView::Partials::PartialRenderer is caching
partials used by each controller as an optimization
• But.. it ends up holding a reference to every single
reloaded version of those controllers
RACK-PERFTOOLS
rack middleware for perftools.rb
gem install rack-

perftools_profiler
github.com/bhb/rack-perftools_profiler
require 'rack/perftools_profiler'
config.middleware.insert(
0,
Rack::PerftoolsProfiler,
:default_printer => 'gif'
)
$ curl http://localhost:3000/__start__
$ curl http://localhost:3000/home
$ curl http://localhost:3000/about
$ curl http://localhost:3000/__stop__
$ curl http://localhost:3000/__data__ -o profile.gif

$ curl http://localhost:3000/__data__?printer=text -o profile.txt
TOOLS MAKE
DEBUGGING EASIER.
LEARN THESE TOOLS.
USE THESE TOOLS.
QUESTIONS?
Aman Gupta
@tmm1

Debugging Ruby

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Debugging Ruby

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DEBUGGING RUBY

TOOLS TO FIX THESE ISSUES.

mayu (flickr) delgrossodotcom (flickr)

lsof -nPp <pid>

FD TYPE NAME json

strace -cp <pid>

% time seconds usecs/call calls errors syscall

epoll_wait(9, {{EPOLLIN, {u32=68841296, u64=68841296}}}, 4096, 50) = 1 <0.033109>

read(22, "GET / HTTP/1.1\r"..., 16384) = 772 <0.0012>

incoming http request

write(5, "SELECT * FROM `table`"..., 56) = 56 <0.0023>

• ruby 1.8 uses signals to schedule its green threads

• debian/redhat compile ruby with --enable-pthread

tcpdump -i eth0 -s 0 -nqA

CPUPROFILE=/tmp/ruby.prof ruby -e' profile

pprof `which ruby` --text /tmp/ruby.prof report

return unless str.sub!(/\A(\d{1,2})/, '')

• known issue: EM+threads =

RUBYOPT="-r`gem which perftools | tail -1`"

pprof.rb /tmp/myrbprof --text

== Sinatra has ended his set (crowd applauds)

Total: 232 samples

• object allocation profiler

ltrace -cp <pid>

ltrace -ttT -e memcpy ruby threaded_em.rb

01:24:49.899414 --- SIGVTALRM (Virtual timer expired) ---

ltrace -F <conf> -bg -x

$ sudo gdb ruby 23611

Program received signal SIGBUS, Bus error.

$ sudo gdb ruby 23611

Program received signal SIGBUS, Bus error.

$ sudo gdb ruby /cores/ruby.core.6.23611.1259781224

gem install gdb.rb

(gdb) ruby eval Thread.current

(gdb) ruby eval Thread.list.size

scope 1641 (0.18%)

30503 unique strings

middleware chain leaking per request

$mongrel_sleeper_thread = Thread.new { loop { sleep 1 } }

5 separate god leaks fixed by Eric

191691 total objects

gem install memprof

let’s use memprof to find it!

tell memprof to dump

tell memprof to dump

mongo query for all

mongo query for all

details for one copy of

“leak” is on line 178

gem install rack-

$ curl http://localhost:3000/__data__ -o profile.gif

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$ curl http://localhost:3000/data -o profile.gif