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  1. [patch] executor and slru dtrace probes

    Zdenek Kotala <zdenek.kotala@sun.com> — 2009-11-13T22:29:41Z

    I attached patch which was already sent on february/april, but it was
lost in time. It is originally from Robert Lor and Theo Schlossnagle.

It contains two DTrace probe groups. One is related to monitoring SLRU
and second is about executor nodes.

I merged it with the head.

Original end of mail thread is here:

http://archives.postgresql.org/pgsql-hackers/2009-04/msg00148.php

	Zdenek

  2. Re: [patch] executor and slru dtrace probes

    Bernd Helmle <mailings@oopsware.de> — 2009-12-07T23:27:34Z

    
--On 13. November 2009 23:29:41 +0100 Zdenek Kotala <Zdenek.Kotala@Sun.COM> 
wrote:

> t contains two DTrace probe groups. One is related to monitoring SLRU
> and second is about executor nodes.
>
> I merged it with the head.
>
> Original end of mail thread is here:
>
> http://archives.postgresql.org/pgsql-hackers/2009-04/msg00148.php

I've started to review this.

It seems to me the attached patch wasn't adjusted or discussed again to 
address Tom's complaints? At least the executor probes contained here hold 
still the same issues mentioned by Tom in the discussion linked here.


-- 
Thanks

	Bernd

  3. Re: [patch] executor and slru dtrace probes

    Zdenek Kotala <zdenek.kotala@sun.com> — 2009-12-08T10:10:44Z

    Dne  8.12.09 00:27, Bernd Helmle napsal(a):
> 
> 
> --On 13. November 2009 23:29:41 +0100 Zdenek Kotala 
> <Zdenek.Kotala@Sun.COM> wrote:
> 
>> t contains two DTrace probe groups. One is related to monitoring SLRU
>> and second is about executor nodes.
>>
>> I merged it with the head.
>>
>> Original end of mail thread is here:
>>
>> http://archives.postgresql.org/pgsql-hackers/2009-04/msg00148.php
> 
> I've started to review this.
> 
> It seems to me the attached patch wasn't adjusted or discussed again to 
> address Tom's complaints? At least the executor probes contained here 
> hold still the same issues mentioned by Tom in the discussion linked here.

I did not make any change. I only revival patch and merge it with head. 
I think that SLRU probes are OK and acceptable.

Tom's issues with executor probes are still there and I expect 
discussion about them. IIRC Theo uses these probes in production.

If you think that it is better I could split patch into two separate 
patches and both can be reviewed separately.

	thanks Zdenek

  4. Re: [patch] executor and slru dtrace probes

    Theo Schlossnagle <jesus@omniti.com> — 2009-12-10T00:08:07Z

    On Dec 8, 2009, at 5:10 AM, Zdenek Kotala wrote:

> Dne  8.12.09 00:27, Bernd Helmle napsal(a):
>> --On 13. November 2009 23:29:41 +0100 Zdenek Kotala <Zdenek.Kotala@Sun.COM> wrote:
>>> t contains two DTrace probe groups. One is related to monitoring SLRU
>>> and second is about executor nodes.
>>> 
>>> I merged it with the head.
>>> 
>>> Original end of mail thread is here:
>>> 
>>> http://archives.postgresql.org/pgsql-hackers/2009-04/msg00148.php
>> I've started to review this.
>> It seems to me the attached patch wasn't adjusted or discussed again to address Tom's complaints? At least the executor probes contained here hold still the same issues mentioned by Tom in the discussion linked here.
> 
> I did not make any change. I only revival patch and merge it with head. I think that SLRU probes are OK and acceptable.
> 
> Tom's issues with executor probes are still there and I expect discussion about them. IIRC Theo uses these probes in production.
> 
> If you think that it is better I could split patch into two separate patches and both can be reviewed separately.

I suppose I see it as a simple thing.  The probes have no performance impact when they are not instrumented.  I've used them on rare occasion to understand which exec nodes are causing which disk accesses.  Seemed pretty darn useful at the time.  There is (of course) some performance overhead when they are enabled, but that is intentionally performed by the operator, so it seems like a non-issue.

Now, there was some indication that there was a better place to probe that would be more comprehensive -- that should be addressed.

--
Theo Schlossnagle
Esoteric Curio -- http://lethargy.org/
OmniTI Computer Consulting, Inc. -- http://omniti.com/

  5. Re: [patch] executor and slru dtrace probes

    Bernd Helmle <mailings@oopsware.de> — 2009-12-10T14:51:34Z

    
--On 8. Dezember 2009 11:10:44 +0100 Zdenek Kotala <Zdenek.Kotala@Sun.COM> 
wrote:

> If you think that it is better I could split patch into two separate
> patches and both can be reviewed separately.

I split up this patch into two separate patches: one for SLRU and one for 
the executor probes. I've done some documentation on the SLRU part, maybe 
you can look over it (to make sure i didn't break anything).

I left the executor probes out of the documentation for now, since it seems 
not to be clear how they would manifest.

Out of curiosity: Why do we want to pass the SlruCtl pointer down to the 
probes? I don't understand what those probes are going to do with those 
pointers, can you explain?

-- 
Thanks

	Bernd

  6. Re: [patch] executor and slru dtrace probes

    Zdenek Kotala <zdenek.kotala@sun.com> — 2009-12-10T15:49:50Z

    Dne 10.12.09 15:51, Bernd Helmle napsal(a):
> 
> 
> --On 8. Dezember 2009 11:10:44 +0100 Zdenek Kotala 
> <Zdenek.Kotala@Sun.COM> wrote:
> 
>> If you think that it is better I could split patch into two separate
>> patches and both can be reviewed separately.
> 
> I split up this patch into two separate patches: one for SLRU and one 
> for the executor probes. I've done some documentation on the SLRU part, 
> maybe you can look over it (to make sure i didn't break anything).
> 
> I left the executor probes out of the documentation for now, since it 
> seems not to be clear how they would manifest.
> 
> Out of curiosity: Why do we want to pass the SlruCtl pointer down to the 
> probes? I don't understand what those probes are going to do with those 
> pointers, can you explain?
> 

You need to determine which SLRU is used. Because SLRUs are initialized 
  during startup  pointer should be same in all backends. If I think 
more about it. Maybe it could be goot to add probe also into 
SimpleLruInit to catch name of SLRUs.

		Zdenek

  7. Re: [patch] executor and slru dtrace probes

    Bernd Helmle <mailings@oopsware.de> — 2009-12-10T16:15:44Z

    
--On 9. Dezember 2009 19:08:07 -0500 Theo Schlossnagle <jesus@omniti.com> 
wrote:

> Now, there was some indication that there was a better place to probe
> that would be more comprehensive -- that should be addressed.

For now there exists no consensus where they should go in. Tom pointed out 
various issues with ExecProcNode() and he's worried about the performance 
penalty those probes might introduce. I admit I'm not very experienced with 
dtrace, but maybe some worries exists because an expensive instrumented 
executor probe can cause forged results?


-- 
Thanks

	Bernd

  8. Re: [patch] executor and slru dtrace probes

    Bernd Helmle <mailings@oopsware.de> — 2009-12-14T12:19:27Z

    
--On 10. Dezember 2009 16:49:50 +0100 Zdenek Kotala <Zdenek.Kotala@Sun.COM> 
wrote:

> You need to determine which SLRU is used. Because SLRUs are initialized
> during startup  pointer should be same in all backends. If I think more
> about it. Maybe it could be goot to add probe also into SimpleLruInit to
> catch name of SLRUs.

Hi Zdenek,

do you plan to work on this further? I was about to mark the SLRU probes as 
ready for committer...

-- 
Thanks

	Bernd

  9. Re: [patch] executor and slru dtrace probes

    Robert Haas <robertmhaas@gmail.com> — 2009-12-14T12:49:34Z

    On Mon, Dec 14, 2009 at 7:19 AM, Bernd Helmle <mailings@oopsware.de> wrote:
> --On 10. Dezember 2009 16:49:50 +0100 Zdenek Kotala <Zdenek.Kotala@Sun.COM>
> wrote:
>
>> You need to determine which SLRU is used. Because SLRUs are initialized
>> during startup  pointer should be same in all backends. If I think more
>> about it. Maybe it could be goot to add probe also into SimpleLruInit to
>> catch name of SLRUs.
>
> Hi Zdenek,
>
> do you plan to work on this further? I was about to mark the SLRU probes as
> ready for committer...

Since the author has pretty much admitted he didn't fix any of the
issues that were raised by the last committer review, I'm a little
confused about why you're asking for another one.

...Robert

  10. Re: [patch] executor and slru dtrace probes

    Bernd Helmle <mailings@oopsware.de> — 2009-12-14T19:33:12Z

    
--On 14. Dezember 2009 07:49:34 -0500 Robert Haas <robertmhaas@gmail.com> 
wrote:

> Since the author has pretty much admitted he didn't fix any of the
> issues that were raised by the last committer review, I'm a little
> confused about why you're asking for another one.

It wasn't clear to me what Zdenek meant with "If I think about it".

-- 
Thanks

	Bernd

  11. Re: [patch] executor and slru dtrace probes

    Bernd Helmle <mailings@oopsware.de> — 2009-12-14T19:42:56Z

    
--On 14. Dezember 2009 20:33:12 +0100 Bernd Helmle <mailings@oopsware.de> 
wrote:

>> Since the author has pretty much admitted he didn't fix any of the
>> issues that were raised by the last committer review, I'm a little
>> confused about why you're asking for another one.
>
> It wasn't clear to me what Zdenek meant with "If I think about it".

Oh, and i was under the opinion the last discussions were about executor 
probes only (note the patch is split up into two parts now, SLRU and 
executor probes). The latter won't be fixed, but it seems the SLRU part at 
least is ready.

-- 
Thanks

	Bernd

  12. Re: [patch] executor and slru dtrace probes

    Zdenek Kotala <zdenek.kotala@sun.com> — 2009-12-14T20:01:47Z

    Bernd Helmle píše v po 14. 12. 2009 v 20:42 +0100:
> 
> --On 14. Dezember 2009 20:33:12 +0100 Bernd Helmle <mailings@oopsware.de> 
> wrote:
> 
> >> Since the author has pretty much admitted he didn't fix any of the
> >> issues that were raised by the last committer review, I'm a little
> >> confused about why you're asking for another one.
> >
> > It wasn't clear to me what Zdenek meant with "If I think about it".
> 
> Oh, and i was under the opinion the last discussions were about executor 
> probes only (note the patch is split up into two parts now, SLRU and 
> executor probes). The latter won't be fixed, but it seems the SLRU part at 
> least is ready.
> 

I would like to add  SimpleLruInit probe. I'm busy with PG packaging,
but I hope that I will send updated version tomorrow.

	Zdenek

  13. Re: [patch] executor and slru dtrace probes

    Greg Smith <greg@2ndquadrant.com> — 2009-12-15T17:10:09Z

    Zdenek Kotala wrote:
> Bernd Helmle píše v po 14. 12. 2009 v 20:42 +0100:
>   
>> Oh, and i was under the opinion the last discussions were about executor 
>> probes only (note the patch is split up into two parts now, SLRU and 
>> executor probes). The latter won't be fixed, but it seems the SLRU part at 
>> least is ready.
>>     
>
> I would like to add  SimpleLruInit probe. I'm busy with PG packaging,
> but I hope that I will send updated version tomorrow.
>   
I'd like to see as many of these DTrace probes as possible make it into 
8.5, and it's great that you've picked up these older ones and updated 
them.  It looks like a lot of progress was made on actually measuring 
the overhead of adding these probes in even when they're not enabled, 
which is good.

But I'm afraid we're already out of time for this one if you're still 
tweaking the probes here.  With a functional change like that, our 
normal process at this point would be to have the reviewer re-evaluate 
things before they head to a committer, and I don't feel like this patch 
is quite at 100% yet--in particular, the probe documentation is 
improving but still a bit rough.  I don't feel like we're quite ready to 
mark this one for commit for this one, and today we really want to clear 
the queue for things for committers to deal with.  Please send that 
updated version, and let's keep working on this into the next 
CommitFest, where it will be in the front of the queue rather than how 
it ended up at the tail of this one just based on its submission date.  
You're not really getting a fair chunk of time here between your review 
and the end here because of problems lining up reviewer time, that 
shouldn't happen next time.

-- 
Greg Smith    2ndQuadrant   Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com  www.2ndQuadrant.com

  14. Re: [patch] executor and slru dtrace probes

    Bernd Helmle <mailings@oopsware.de> — 2009-12-15T22:10:36Z

    
--On 15. Dezember 2009 12:10:09 -0500 Greg Smith <greg@2ndquadrant.com> 
wrote:

> But I'm afraid we're already out of time for this one if you're still
> tweaking the probes here.  With a functional change like that, our
> normal process at this point would be to have the reviewer re-evaluate
> things before they head to a committer, and I don't feel like this patch
> is quite at 100% yet--in particular, the probe documentation is improving
> but still a bit rough.  I don't feel like we're quite ready to mark this
> one for commit for this one, and today we really want to clear the queue
> for things for committers to deal with.  Please send that updated
> version, and let's keep working on this into the next CommitFest, where
> it will be in the front of the queue rather than how it ended up at the
> tail of this one just based on its submission date.  You're not really
> getting a fair chunk of time here between your review and the end here
> because of problems lining up reviewer time, that shouldn't happen next
> time.

That seems reasonable.

I hope i could contribute something, even this was the first time i got my 
hands on reviewing this DTrace thingie.

-- 
Thanks

	Bernd

  15. Re: [patch] executor and slru dtrace probes

    Zdenek Kotala <zdenek.kotala@sun.com> — 2009-12-23T14:37:21Z

    Greg Smith píše v út 15. 12. 2009 v 12:10 -0500:

>  Please send that updated version, and let's keep working on this into
> the next CommitFest, where it will be in the front of the queue rather
> than how it ended up at the tail of this one just based on its
> submission date.  You're not really getting a fair chunk of time here
> between your review and the end here because of problems lining up
> reviewer time, that shouldn't happen next time.

Make sense. 

	Zdenek