Comments on: Advanced Oracle Troubleshooting Guide, Part 2: No magic is needed, systematic approach will do

By: Patryk

Patryk — Sat, 06 Feb 2010 01:01:37 +0000

Hi Tanel,

I never seen such a deep investigation.
Keep going man.

By: Khalid Azmi

Khalid Azmi — Sat, 09 Jan 2010 07:39:50 +0000

Your blog is just WOW, why didn’t i come across this earlier. I think i read somewhere in your blog that you were planning to write a book but then dropped it :(

By: tanelp

tanelp — Thu, 27 Mar 2008 13:10:41 +0000

Newer versions of HP-UX should have the pstack utility.

Otherwise you should be able to do the same with a debugger like dbx or gdb (whichever is present on your machine).

On which HP-UX version are you?

By: qihua

qihua — Thu, 27 Mar 2008 06:48:37 +0000

how hpux? what kind of tool hpux provided could do the same investigation

By: Advanced Oracle Troubleshooting Guide, Part 3: More adventures in process stack « Tanel Poder’s blog: Core IT for geeks and pros

Wed, 05 Sep 2007 16:50:55 +0000

[...] So, reading the bold sections from bottom up (and using the Metalink note 175982.1 I’ve mentioned earlier) [...]

By: tanelp

tanelp — Sat, 01 Sep 2007 09:13:42 +0000

Yep, Linux /proc filesystem allows you to write a pstack utility reading directly from /proc//mem too, but looks like it’s not written yet :)

By: amit poddar

amit poddar — Fri, 31 Aug 2007 20:45:32 +0000

Linux also has a /proc file system.

Do you know why they chose a intrusive method instead of reading it of from the /proc file system ?

By: tanelp

tanelp — Fri, 31 Aug 2007 16:22:01 +0000

Hi Amit,

Which version of AIX?

In 5.2+ it should be pretty safe as it uses /proc filesystem for reading process stack (earlier versions may use /proc too)

The procstack command briefly suspends the probed process (just like scheduler does when timeslice has expired) and reads stack through /proc filesystem.

This is fast and non-intrusive.

On linux however the pstack is just a wrapper around gdb command. So gdb starts up, attaches to the process, suspends it, loads a bunch of libraries and reads the process stack using slow ptrace() system calls. Also I’ve seen the pstack crashing the probed process in some circumstances (like when running a strace on the pstack process itself and attaching to target)

By: amit poddar

amit poddar — Fri, 31 Aug 2007 14:53:10 +0000

Hi,

Do you know how AIX’s procstack work.
Is it very intrusive ?

By: tanelp

tanelp — Wed, 29 Aug 2007 16:30:53 +0000

Thanks to all for the comments.
John, yep I’m already using v$session_wait.state which in turn is also decoded from x$ksusecst’s time_waited equivalent column (and from x$kslwt in 11g).
I do prefer to use the STATE column though, it’s easier to remember: waiting = waiting, anything else = NOT waiting :)

Jeroen, the seconds_in_wait column is increased for long waits in v$session_wait. I don’t use the time_waited column directly at all when diagnosing performance issues, as seconds_in_wait shows the time spent in current wait and if Im interested in wait history then I either query v$session_wait_history for last 10 events or use v$session_event or Session Snapper…