Обсуждение: gdb with postgres

On Mon, Jun 6, 2011 at 1:13 PM, HuangQi <huangqiyx@gmail.com> wrote:
> Hi,
>    I was using gdb to debug postgres. In order to debug the backend of
> running query, I start postgres first and use "select * from
> pg_backend_pid()" to ask for backend pid. Then I start gdb in another bash
> window with "gdb postgres" and attach the pid obtained above and set the
> breakpoint. Then I run the query from the first window. However, the
> debugging precess which is shown below is not going to the breakpoint. I
> tried many different breakpoints, but it always start from the 305
> client_read_ended().
>

Please compile with -O0 -g flags to see all the debug symbols.

CFLAGS="-O0 -g" ./configure --enable-debug

Thanks,
Pavan

--
Pavan Deolasee
EnterpriseDB     http://www.enterprisedb.com

On Mon, Jun 6, 2011 at 3:43 AM, HuangQi <huangqiyx@gmail.com> wrote:
> Hi,
>    I was using gdb to debug postgres. In order to debug the backend of
> running query, I start postgres first and use "select * from
> pg_backend_pid()" to ask for backend pid. Then I start gdb in another bash
> window with "gdb postgres" and attach the pid obtained above and set the
> breakpoint. Then I run the query from the first window. However, the
> debugging precess which is shown below is not going to the breakpoint. I
> tried many different breakpoints, but it always start from the 305
> client_read_ended().
>
> GNU gdb 6.6
> Copyright (C) 2006 Free Software Foundation, Inc.
> GDB is free software, covered by the GNU General Public License, and you are
> welcome to change it and/or distribute copies of it under certain
> conditions.
> Type "show copying" to see the conditions.
> There is absolutely no warranty for GDB.  Type "show warranty" for details.
> This GDB was configured as "sparc-sun-solaris2.10"...
> (gdb) b qp_add_paths_to_joinrel
> Breakpoint 1 at 0x1a6744: file joinpath.c, line 67.
> (gdb) attach 23903
> Attaching to program `/usrlocal/pgsql/bin/postgres', process 23903
> Retry #1:
> Retry #2:
> Retry #3:
> Retry #4:
> [New LWP 1]
> 0xff0cbaa4 in _rt_boot () from /usr/lib/ld.so.1
> (gdb) n
> Single stepping until exit from function _rt_boot,
> which has no line number information.
> secure_read (port=0x4a7760, ptr=0x455948, len=8192) at be-secure.c:305
> 305                     client_read_ended();
> (gdb) n
> pq_recvbuf () at pqcomm.c:767
> 767                     if (r < 0)
> (gdb) n
> 769                             if (errno == EINTR)
> (gdb) n
> 782                     if (r == 0)
> (gdb) n
> 788                             return EOF;
> (gdb) n
> 791                     PqRecvLength += r;
> (gdb)
> Any one know what is going wrong? BTW, as you can see, the system is
> solaris.

Perhaps you want "c" for "continue" rather than "n" for "next".

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

On Mon, Jun 6, 2011 at 9:47 AM, HuangQi <huangqiyx@gmail.com> wrote:
> If I enter c, gdb will directly finish executing this process and current
> query will finish. Furthermore, if I enter next query, gdb will not debug it
> and stay in continue status.

Hmm, that must mean your breakpoint isn't properly set.

Instead of doing gdb postgres and then using attach, try just doing
gdb -p PIDNAME, then set your breakpoint, then continue.  That's how
I've always done it, anyway...

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

HuangQi <huangqiyx@gmail.com> wrote:
>>> (gdb) b qp_add_paths_to_joinrel
>>> Breakpoint 1 at 0x1a6744: file joinpath.c, line 67.
>>> (gdb) attach 23903
> If I enter c, gdb will directly finish executing this process and
> current query will finish.
Are you absolutely sure that running your query will result in a
call to this function?
-Kevin