Performance Monitoring
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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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
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