Search Postgresql Archives

Re: segmentation fault postgres 9.3.5 core dump perlu related ?

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hi Alan,

 

Thanks for your  input.

 

My initial simplistic stress  test ( two connections calling same suspect  function in a loop ) has failed in causing the problem albeit I have not used  any  range of inputs for the possible parameters. Given your thoughts on the the internal mechnanics it seems unlikely it is competing sessions.    I’ll see about varying and logging  arguments in future testing.   Reproducing is 90 % of the battle and

unfortunately we are losing on that front currently.

 

When I type (gdb) info threads  on the most recent core file I see:

* 1 Thread 802c06400 (LWP 101353/postgres)  0x00000000005756b8 in ExecProcNode ()

Not sure that fits with your expectations.

 

We only have two invoked perl functions in the database both of which are plperlu.  These functions are

both invoked at least once  in a normal usage  scenario,  which makes the infrequency of the segmentation fault puzzling.

 

 

Regards

 

 

Dave

 

 

 

 

From: Alex Hunsaker [mailto:badalex@xxxxxxxxx]
Sent: Thursday, January 29, 2015 12:58 AM
To: Day, David
Cc: pgsql-general@xxxxxxxxxxxxxx
Subject: Re: [GENERAL] segmentation fault postgres 9.3.5 core dump perlu related ?

 

 

On Wed, Jan 28, 2015 at 1:23 PM, Day, David <dday@xxxxxxxxxx> wrote:

It has been some time since we have seen this problem.
See earlier  message on this subject/thread  for the suspect  plperl function executing
at the time of the core.

Someone on our development team  suggested it might relate to some build options of perl.
In particular MULTIPLICITY or THREADS . We can have this perl fx executing on
two different connections/sessions at the same time.

 

Hrm, I can't see how >1 connections/sessions could tickle the bug. Or THREADS/MULTIPLICITY, short of some perl bug. Each backend is its own process and so each perl interpreter is isolated at from each other at that level. IOW each new connection has its very own perl interpreter that has no shared state with any of the others (short of using $_SHARED). But hey, if your testing finds it is easier to trigger with more connections, it just makes the bug more interesting :).

 

open as use use it should just be standard pipe(); fork(); exec(); dance. And I'm fairly certain perl does not do anything magic like making a thread behind the scene. In gdb you could also try "info threads", just to see if somehow a thread did created.

 

Multiplicity should only come into play if you use plperl and plperlu in the same session (without it, it should error out with "Cannot allocate multiple Perl interpreters on this platform").

 

 


I believe below is an valid stack dump:

Core was generated by `postgres'.
Program terminated with signal 11, Segmentation fault.
(gdb) bt
#0  0x000000080bfa50a3 in Perl_fbm_instr () from /usr/local/lib/perl5/5.18/mach/CORE/libperl.so.5.18
#1  0x000000080c00ff93 in Perl_re_intuit_start () from /usr/local/lib/perl5/5.18/mach/CORE/libperl.so.5.18
#2  0x000000080bfc27a2 in Perl_pp_match () from /usr/local/lib/perl5/5.18/mach/CORE/libperl.so.5.18

 

This sure makes it look like it is segfaulting on some kind of regex /not/ open.

 

Any chance you could come up with a reproducible test case? I suspect the inputs to the function might help narrow it down to something reproducible. Maybe log the arguments at the start of the function? Or perhaps in your middleware when calling the function crashes, log how it was called?

 


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Index of Archives]     [Postgresql Jobs]     [Postgresql Admin]     [Postgresql Performance]     [Linux Clusters]     [PHP Home]     [PHP on Windows]     [Kernel Newbies]     [PHP Classes]     [PHP Books]     [PHP Databases]     [Postgresql & PHP]     [Yosemite]
  Powered by Linux