Req #64709 [Opn->Wfx]: Get a PHP stack trace on process signal
Edit report at https://bugs.php.net/bug.php?id=64709&edit=1
ID: 64709
Updated by: rasmus@php.net
Reported by: williama_lovaton at coomeva dot com dot co
Summary: Get a PHP stack trace on process signal
-Status: Open
+Status: Wont fix
Type: Feature/Change Request
Package: Performance problem
Operating System: Linux
PHP Version: Irrelevant
Block user comment: N
Private report: N
New Comment:
Why not just attach gdb to the process and do a bt? I do that all the time. If
it is in an internal PHP function you will see zif_funcname where zif = zend
internal function. If it is in a userspace function it is slightly harder. You
need to install the .gdbinit gdb macros from https://raw.github.com/php/php-
src/master/.gdbinit in your home directory and you can then type zbacktrace and
you get the entire PHP call stack.
The problem with adding a signal handler is that PHP is often not a standalone
thing. It is embedded inside Apache or other mechanisms that own the signal
handling layer. Any signal we pick would conflict with something at the server
level and this is a rather low-level feature for developers who know what they
are doing anyway. If they know what they are doing they should be able to
navigate gdb.
Previous Comments:
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[2013-04-25 20:29:27] williama_lovaton at coomeva dot com dot co
Thanks for your comments. I'm using both tools (xdebug and XHProf), they are excellent but
xdebug has a big performance impact even if you are not using it and right now I can't afford
that on production, I use it in my development environment though. XHProf is enabled on production
and it is really great but as far as I know it can only show me the data after the fact.
The specific thing about this feature request is that I want to see where a given process is stuck
while it's still serving the request. For example, with gstack I can see the process is stuck
in the OCIExecute() function executing a query or in OCIStmtFetch() function fetching the data
(I'm using an Oracle database). But I can't see which PHP function, and hence the query,
is causing the slowness.
This have been asked before by other people under different scenarios:
http://stackoverflow.com/questions/14261821/get-a-stack-trace-of-a-hung-php-script
But there is no satisfying answer.
I was just wondering if this feature is at all doable.
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[2013-04-25 19:11:18] sixd@php.net
Also review XHProf & XHGui
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[2013-04-25 17:19:16] ab@php.net
With performance - what about profiling with xdebug or zend?
The other were for sure possible catching some signal. Though dunno yet if the same gdb
functionality is available on windows.
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[2013-04-25 16:22:02] williama_lovaton at coomeva dot com dot co
Description:
------------
I'm not sure if this is possible to implement or if it's implemented now but I'd like
a way to get a PHP stack trace of a running process on any given time (may be using a process signal
with kill).
This would be very similar to what you can do with Java, you do a "kill -3 <pid>"
but the process doesn't die, instead it outputs a full backtrace of Java code of every thread
and the current state.
You can do something similar now using the gstack command from GDB but you'll get a stack trace
from the C code. I'd like to be able to get a stack trace but from the PHP code so that I can
analyze where is the exact point in the program where my web app is running slow or getting stuck.
My web app is instrumented and I can get logs from slow functions but this is information I get
after the fact. With this feature request it would be possible to get the information exactly when
it is happening.
Is this possible? If so, would it be possible to make it work if PHP is being run as an Apache
module?
Thanks a lot for your time.
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