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* Re: Performance monitoring
@ 2007-05-12 21:26 ` Joshua D. Drake <jd@commandprompt.com>
2007-05-12 23:24 ` Re: Performance monitoring Greg Smith <gsmith@gregsmith.com>
2007-05-13 04:41 ` Re: Performance monitoring Neil Conway <neilc@samurai.com>
1 sibling, 2 replies; 10+ messages in thread
From: Joshua D. Drake @ 2007-05-12 21:26 UTC (permalink / raw)
To: Jim C. Nasby <decibel@decibel.org>; +Cc: Heikki Linnakangas <heikki@enterprisedb.com>; Greg Smith <gsmith@gregsmith.com>; pgsql-hackers
> Not to beat a dead horse, but do we really want to force folks to be
> parsing logs for performance monitoring? Especially if that log parsing
> is just going to result in data being inserted into a table anyway?
>
> I know there's concern about performance of the stats system and maybe
> that needs to be addressed, but pushing users to log parsing is a lot of
> extra effort, non-standard, likely to be overlooked, and doesn't play
> well with other tools. It also conflicts with all the existing
> statistics framework.
One thing that doesn't seemed to be being looked at it is the cost of
logging. Logging is very expensive. I don't know if it is more expensive
than the stats system, but you can cut your tps in half by having any
level of verbose logging on.
Yes that can be offset by pushing the logging to another spindle, and
being careful about what you are logging but still.
Either way, we are taking the hit, it is just a matter of where. IMO it
would be better to have the information in the database where it makes
sense, than pushing out to a log that:
A. Will likely be forgotten
B. Is only accessible if you have shell access to the machine (not as
common as all of us would like to think)
Sincerely,
Joshua D. Drake
--
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^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Performance monitoring
2007-05-12 21:26 ` Re: Performance monitoring Joshua D. Drake <jd@commandprompt.com>
@ 2007-05-12 23:24 ` Greg Smith <gsmith@gregsmith.com>
1 sibling, 0 replies; 10+ messages in thread
From: Greg Smith @ 2007-05-12 23:24 UTC (permalink / raw)
To: pgsql-hackers
On Sat, 12 May 2007, Joshua D. Drake wrote:
> One thing that doesn't seemed to be being looked at it is the cost of
> logging.
If any of this executed at something like the query level, sure, that
would be real important. The majority of the logging I suggested here is
of things that happen at checkpoint time. The presumption is that the
overhead of that is considerably greater than writing a log line or even
five.
The least intensive event I would like to be loggable is when a new WAL
segment is created and cleared, which is again a pretty small bit of log
compared to the 16MB write. I wouldn't mind seeing that exposed under
pg_stats instead, just had more interesting things to statify first.
--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD
^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Performance monitoring
2007-05-12 21:26 ` Re: Performance monitoring Joshua D. Drake <jd@commandprompt.com>
@ 2007-05-13 04:41 ` Neil Conway <neilc@samurai.com>
1 sibling, 0 replies; 10+ messages in thread
From: Neil Conway @ 2007-05-13 04:41 UTC (permalink / raw)
To: Joshua D. Drake <jd@commandprompt.com>; +Cc: Jim C. Nasby <decibel@decibel.org>; Heikki Linnakangas <heikki@enterprisedb.com>; Greg Smith <gsmith@gregsmith.com>; pgsql-hackers
On Sat, 2007-12-05 at 14:26 -0700, Joshua D. Drake wrote:
> Either way, we are taking the hit, it is just a matter of where. IMO it
> would be better to have the information in the database where it makes
> sense, than pushing out to a log
If performance monitoring information is provided as a database object,
what would the right interface be? IMHO the problem with cleanly
presenting monitoring information within a normal database system is
that this sort of data is fundamentally dynamic and continuous: to
determine how the performance of the system changes over time, you need
to repeatedly rescan the table/view/SRF and recompute your analysis
essentially from scratch. Trying to get even simple information like
"queries per second" from pg_stat_activity is an example of how this can
be painful.
<plug>
BTW, if the system included the concept of a continuous data *stream* as
a kind of database object, this problem would be much more tractable :)
In fact, there is some code in a version of TelegraphCQ that exposes
various information about the runtime state of the system as a set of
system-defined data streams -- like any other stream, users could then
use those streams in arbitrary queries.
</plug>
-Neil
^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Performance monitoring
@ 2007-05-13 06:54 ` Heikki Linnakangas <heikki@enterprisedb.com>
2007-05-13 15:37 ` Re: Performance monitoring Magnus Hagander <magnus@hagander.net>
2007-05-13 20:46 ` Re: Performance monitoring Jim C. Nasby <decibel@decibel.org>
2007-05-14 11:12 ` Re: Performance monitoring Zdenek Kotala <Zdenek.Kotala@Sun.COM>
1 sibling, 3 replies; 10+ messages in thread
From: Heikki Linnakangas @ 2007-05-13 06:54 UTC (permalink / raw)
To: Jim C. Nasby <decibel@decibel.org>; +Cc: Greg Smith <gsmith@gregsmith.com>; pgsql-hackers
Jim C. Nasby wrote:
> Moving to -hackers.
>
> On Fri, May 11, 2007 at 04:37:44PM +0100, Heikki Linnakangas wrote:
>>> If you know when the checkpoint ended, and you know how long each of the
>>> pieces took, you can reconstruct the other times easily. The way you
>>> describe this it is true--that the summary is redundant given the
>>> detail--but if you put yourself in the shoes of a log file parser the
>>> other way around is easier to work with. Piecing together log entries
>>> is a pain, splitting them is easy.
>>>
>>> If I had to only keep one line out of this, it would be the one with the
>>> summary. It would be nice to have it logged at INFO.
>> Yeah, if we have the summary line we don't need the other lines and vice
>> versa. I have sympathy for parsing log files, I've done that a lot in
>> the past and I can see what you mean. Having the individual lines is
>> nice when you're monitoring a running system; you don't get the summary
>> line until the checkpoint is finished. I suppose we can have both the
>> individual lines and the summary, the extra lines shouldn't hurt anyone,
>> and you won't get them unless you turn on the new log_checkpoints
>> parameter anyway.
>
> Not to beat a dead horse, but do we really want to force folks to be
> parsing logs for performance monitoring? Especially if that log parsing
> is just going to result in data being inserted into a table anyway?
>
> I know there's concern about performance of the stats system and maybe
> that needs to be addressed, but pushing users to log parsing is a lot of
> extra effort, non-standard, likely to be overlooked, and doesn't play
> well with other tools. It also conflicts with all the existing
> statistics framework.
There is two counters for checkpoints in pgstats, the number of timed
(triggered by checkpoint_timeout) and requested (triggered by
checkpoint_segments) checkpoints.
Maybe we should improve the stats system so that we can collect events
with timestamps and durations, but in my experience log files actually
are the most reliable and universal way to collect real-time performance
information. Any serious tool has a generic log parser. The other
alternative is SNMP. I welcome the efforts on pgsnmpd..
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Performance monitoring
2007-05-13 06:54 ` Re: Performance monitoring Heikki Linnakangas <heikki@enterprisedb.com>
@ 2007-05-13 15:37 ` Magnus Hagander <magnus@hagander.net>
2 siblings, 0 replies; 10+ messages in thread
From: Magnus Hagander @ 2007-05-13 15:37 UTC (permalink / raw)
To: Heikki Linnakangas <heikki@enterprisedb.com>; +Cc: Jim C. Nasby <decibel@decibel.org>; Greg Smith <gsmith@gregsmith.com>; pgsql-hackers
Heikki Linnakangas wrote:
>>> Yeah, if we have the summary line we don't need the other lines and
>>> vice versa. I have sympathy for parsing log files, I've done that a
>>> lot in the past and I can see what you mean. Having the individual
>>> lines is nice when you're monitoring a running system; you don't get
>>> the summary line until the checkpoint is finished. I suppose we can
>>> have both the individual lines and the summary, the extra lines
>>> shouldn't hurt anyone, and you won't get them unless you turn on the
>>> new log_checkpoints parameter anyway.
>>
>> Not to beat a dead horse, but do we really want to force folks to be
>> parsing logs for performance monitoring? Especially if that log parsing
>> is just going to result in data being inserted into a table anyway?
>>
>> I know there's concern about performance of the stats system and maybe
>> that needs to be addressed, but pushing users to log parsing is a lot of
>> extra effort, non-standard, likely to be overlooked, and doesn't play
>> well with other tools. It also conflicts with all the existing
>> statistics framework.
>
> There is two counters for checkpoints in pgstats, the number of timed
> (triggered by checkpoint_timeout) and requested (triggered by
> checkpoint_segments) checkpoints.
>
> Maybe we should improve the stats system so that we can collect events
> with timestamps and durations, but in my experience log files actually
> are the most reliable and universal way to collect real-time performance
> information. Any serious tool has a generic log parser. The other
> alternative is SNMP. I welcome the efforts on pgsnmpd..
pgsnmpd can't provide any information that's not in the backend. Unless
we'd turn it into a log parser, which is not really something I think is
a good idea.
Log files are great for one kind of thing, "live statistics" through
SNMP or the statistics collector for another kind. It only gets wrong
when you put them in the wrong place. Things you poll regularly makes a
lot more sense in some kind of live view than in a log file.
//Magnus
^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Performance monitoring
2007-05-13 06:54 ` Re: Performance monitoring Heikki Linnakangas <heikki@enterprisedb.com>
@ 2007-05-13 20:46 ` Jim C. Nasby <decibel@decibel.org>
2 siblings, 0 replies; 10+ messages in thread
From: Jim C. Nasby @ 2007-05-13 20:46 UTC (permalink / raw)
To: Heikki Linnakangas <heikki@enterprisedb.com>; +Cc: Greg Smith <gsmith@gregsmith.com>; pgsql-hackers
On Sun, May 13, 2007 at 07:54:20AM +0100, Heikki Linnakangas wrote:
> Maybe we should improve the stats system so that we can collect events
> with timestamps and durations, but in my experience log files actually
> are the most reliable and universal way to collect real-time performance
> information. Any serious tool has a generic log parser. The other
> alternative is SNMP. I welcome the efforts on pgsnmpd..
Having timing information in the stats system would be useful, but I'm
not sure how it could actually be done. But at least if the information
is in the stats system it's easy to programatically collect and process.
SNMP is just one example of that (fwiw I agree with Magnus that it
probably doesn't make sense to turn pgsnmpd into a log parser...)
--
Jim Nasby decibel@decibel.org
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Performance monitoring
2007-05-13 06:54 ` Re: Performance monitoring Heikki Linnakangas <heikki@enterprisedb.com>
@ 2007-05-14 11:12 ` Zdenek Kotala <Zdenek.Kotala@Sun.COM>
2 siblings, 0 replies; 10+ messages in thread
From: Zdenek Kotala @ 2007-05-14 11:12 UTC (permalink / raw)
To: Heikki Linnakangas <heikki@enterprisedb.com>; +Cc: Jim C. Nasby <decibel@decibel.org>; Greg Smith <gsmith@gregsmith.com>; pgsql-hackers
Heikki Linnakangas napsal(a):
> Jim C. Nasby wrote:
>
> There is two counters for checkpoints in pgstats, the number of timed
> (triggered by checkpoint_timeout) and requested (triggered by
> checkpoint_segments) checkpoints.
>
> Maybe we should improve the stats system so that we can collect events
> with timestamps and durations, but in my experience log files actually
> are the most reliable and universal way to collect real-time performance
> information. Any serious tool has a generic log parser. The other
> alternative is SNMP. I welcome the efforts on pgsnmpd..
Whats about add some DTrace probes?
Zdenek
^ permalink raw reply [nested|flat] 10+ messages in thread
* Performance Monitoring
@ 2007-06-15 16:22 Umar Farooq <umarfm13@hotmail.com>
2007-06-15 17:29 ` Re: Performance Monitoring Greg Smith <gsmith@gregsmith.com>
0 siblings, 1 reply; 10+ messages in thread
From: Umar Farooq @ 2007-06-15 16:22 UTC (permalink / raw)
To: pgsql-hackers
Hello All,Recently, I have been involved in some work that requires me to monitor low level performance counters for pgsql. Specifically, when I execute a particular query I want to be able to tell how many system calls get executed on behalf of that query and time of each sys call. The idea is to provide a break down of the total query running time in terms of CPU time (user+system) and IO (wait time + service time) and any other contributing factors.I have been using various performance monitoring tool in linux including vmstat, mpstat, iostat and strace(to monitor system calls). Surprisingly, no matter what type of query I execute, when I use strace to monitor the system calls generated they turn out to be the same for ALL sorts of queries. Now this could happen because (a) the tool (strace) is not robust (b) something the pgsql code is doing that eludes strace. At this point I have been unable to narrow it down. Any help in this regard will be greatly appreciated. Also if somebody knows a better way of achieving the same goal please let me know.Thanks for reading.-Umar
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^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Performance Monitoring
2007-06-15 16:22 Performance Monitoring Umar Farooq <umarfm13@hotmail.com>
@ 2007-06-15 17:29 ` Greg Smith <gsmith@gregsmith.com>
2007-06-17 04:30 ` Re: Performance Monitoring Robert Treat <xzilla@users.sourceforge.net>
0 siblings, 1 reply; 10+ messages in thread
From: Greg Smith @ 2007-06-15 17:29 UTC (permalink / raw)
To: pgsql-hackers
On Fri, 15 Jun 2007, Umar Farooq wrote:
> Surprisingly, no matter what type of query I execute, when I use strace
> to monitor the system calls generated they turn out to be the same for
> ALL sorts of queries.
How are you calling strace? The master postgres progress forks off new
processes for each of the clients, you need to make sure you include stats
from all of them as well to get anything.
I normally use
strace -c -f -p [main postgres process]
which is helpful to collecte basic info, but even that's not quite right;
you don't get the work done by the other proceses (logger, writer, stats
collector). To get everything, you need to start some process that you
attach strace to like this, then have that process start the server.
I haven't found strace to be a great tool for this type of work. You
might take at look at systemtap instead (
http://sourceware.org/systemtap/wiki ) which is a bit immature but is
going the right direction.
I will now bow my head and wait for someone to suggest you move to an OS
that supports dtrace.
--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD
^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Performance Monitoring
2007-06-15 16:22 Performance Monitoring Umar Farooq <umarfm13@hotmail.com>
2007-06-15 17:29 ` Re: Performance Monitoring Greg Smith <gsmith@gregsmith.com>
@ 2007-06-17 04:30 ` Robert Treat <xzilla@users.sourceforge.net>
0 siblings, 0 replies; 10+ messages in thread
From: Robert Treat @ 2007-06-17 04:30 UTC (permalink / raw)
To: pgsql-hackers; +Cc: Greg Smith <gsmith@gregsmith.com>
On Friday 15 June 2007 13:29, Greg Smith wrote:
> On Fri, 15 Jun 2007, Umar Farooq wrote:
> > Surprisingly, no matter what type of query I execute, when I use strace
> > to monitor the system calls generated they turn out to be the same for
> > ALL sorts of queries.
>
> How are you calling strace? The master postgres progress forks off new
> processes for each of the clients, you need to make sure you include stats
> from all of them as well to get anything.
>
> I normally use
>
> strace -c -f -p [main postgres process]
>
> which is helpful to collecte basic info, but even that's not quite right;
> you don't get the work done by the other proceses (logger, writer, stats
> collector). To get everything, you need to start some process that you
> attach strace to like this, then have that process start the server.
>
> I haven't found strace to be a great tool for this type of work. You
> might take at look at systemtap instead (
> http://sourceware.org/systemtap/wiki ) which is a bit immature but is
> going the right direction.
>
> I will now bow my head and wait for someone to suggest you move to an OS
> that supports dtrace.
>
You know that's what I was thinking :-)
--
Robert Treat
Build A Brighter LAMP :: Linux Apache {middleware} PostgreSQL
^ permalink raw reply [nested|flat] 10+ messages in thread
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Thread overview: 10+ messages (download: mbox mbox.gz follow: Atom feed)
-- links below jump to the message on this page --
2007-05-12 21:26 ` Joshua D. Drake <jd@commandprompt.com>
2007-05-12 23:24 ` Greg Smith <gsmith@gregsmith.com>
2007-05-13 04:41 ` Neil Conway <neilc@samurai.com>
2007-05-13 06:54 ` Heikki Linnakangas <heikki@enterprisedb.com>
2007-05-13 15:37 ` Magnus Hagander <magnus@hagander.net>
2007-05-13 20:46 ` Jim C. Nasby <decibel@decibel.org>
2007-05-14 11:12 ` Zdenek Kotala <Zdenek.Kotala@Sun.COM>
2007-06-15 16:22 Performance Monitoring Umar Farooq <umarfm13@hotmail.com>
2007-06-15 17:29 ` Re: Performance Monitoring Greg Smith <gsmith@gregsmith.com>
2007-06-17 04:30 ` Re: Performance Monitoring Robert Treat <xzilla@users.sourceforge.net>
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