We have the 4 core machine. However, these numbers are taken during a
benchmark, not normal work load. So the output should display the system
being working fully ;)
So its postgres doing a lot of work and you already had a look at the
usrcall for that.
The benchmark just tries to do the queries for "random page visits".
This totals up to about some 80 different queries being executed with
mostly random parameters. The workload is generated using php so there
are no connection pools, nor prepared statements.
The queries vary, but are all relatively lightweight queries with less
than 6 or 7 joinable tables. Almost all queries can use indexes. Most
tables are under a few MB of data, although there are a few larger than
that. Most records are relatively small, consisting of mostly numbers
(id's and such).
The results presented here was with 25 concurrent connections.
Best regards,
Arjen
Jignesh K. Shah wrote:
You usertime is way too high for T2000...
If you have a 6 core machine with 24 threads, it says all 24 threads are
reported as being busy with iostat output.
Best way to debug this is use
prstat -amL
(or if you are dumping it in a file prstat -amLc > prstat.txt)
and find the pids with high user cpu time and then use the usrcall.d on
few of those pids.
Also how many database connections do you have and what's the type of
query run by each connection?
-Jignesh
Arjen van der Meijden wrote:
Hi Jignesh,
The settings from that 'special T2000 dvd' differed from the
recommended settings on the website you provided. But I don't see much
difference in performance with any of the adjustments, it appears to
be more or less the same.
Here are a few iostat lines by the way:
sd0 sd1 sd2 nfs1 cpu
kps tps serv kps tps serv kps tps serv kps tps serv us sy wt id
7 1 12 958 50 35 0 0 7 0 0 0 13 1 0 85
0 0 0 2353 296 3 0 0 0 0 0 0 92 7 0 1
0 0 0 2062 326 2 0 0 0 0 0 0 93 7 0 0
1 1 1 1575 350 0 0 0 0 0 0 0 92 7 0 1
0 0 0 1628 362 0 0 0 0 0 0 0 92 8 0 1
It appears to be doing a little less kps/tps on sd1 when I restore my
own postgresql.conf-settings. (default wal/checkpoints, 20k buffers,
2k work mem).
Is it possible to trace the stack's for semsys, like the
memcpy-traces, or are those of no interest here?
Best regards,
Arjen
On 16-5-2006 17:52, Jignesh K. Shah wrote:
Hi Arjen,
Can you send me my colleagues's names in a private email?
One of the drawbacks of the syscall.d script is relative timings and
hence if system CPU usage is very low, it gives the relative
weightage about what portion in that low is associated with what
call.. So even if you have say..1% system time.. it says that most of
it was IO related or semsys related. So iostat output with -c option
to include CPU times helps to put it in the right perspective.
Also do check the tunables mentioned and make sure they are set.
Regards,
Jignesh
Arjen van der Meijden wrote:
Hi Jignesh,
Jignesh K. Shah wrote:
Hi Arjen,
Looking at your outputs...of syscall and usrcall it looks like
* Spending too much time in semsys .... which means you have too
many connections and they are contending to get a lock.. which is
potentially the WAL log lock
* llseek is high which means you can obviously gain a bit with the
right file system/files tuning by caching them right.
Have you set the values for Solaris for T2000 tuned for Postgresql?
Not particularly, we got a "special T2000 Solaris dvd" from your
colleagues here in the Netherlands and installed that (actually one
of your colleagues did). Doing so all the "better default"
/etc/system-settings are supposed to be set. I haven't really
checked that they are, since two of your colleagues have been
working on it for the mysql-version of the benchmark and I assumed
they'd have verified that.
Check out the tunables from the following URL
http://www.sun.com/servers/coolthreads/tnb/applications_postgresql.jsp
Try specially the /etc/system and postgresql.conf changes and see
if it changes/improves your performance.
I will see that those tunables are verified to be set.
I am a bit surprised though about your remarks, since they'd point
at the I/O being in the way? But we only have about 600k/sec i/o
according to vmstat. The database easily fits in memory.
In total I logged about 500k queries of which only 70k where
altering queries, of which almost all where inserts in log-tables
which aren't actively read in this benchmark.
But I'll give it a try.
Best regards,
Arjen
Arjen van der Meijden wrote:
Hi List,
In the past few weeks we have been developing a read-heavy
mysql-benchmark to have an alternative take at
cpu/platform-performance. Not really to have a look at how fast
mysql can be.
This benchmark runs on mysql 4.1.x, 5.0.x and 5.1.x and is
modelled after our website's production database and the load
generated on it is modelled after a simplified version of our
visitor behaviour.
Long story short, we think the test is a nice example of the
relatively lightweight, read-heavy webapplications out there and
therefore decided to have a go at postgresql as well.
Of course the queries and indexes have been adjusted to (by our
knowledge) best suit postgresql, while maintaining the same output
to the application/interface layer. While the initial structure
only got postgresql at about half the performance of mysql 4.1.x,
the current version of our postgresql-benchmark has quite similar
results to mysql 4.1.x, but both are quite a bit slower than 5.0.x
(I think its about 30-40% faster).
Since the results from those benchmarks are not yet public (they
will be put together in a story at our website), I won't go into
too much details about this benchmark.
Currently we're having a look at a Sun T2000 and will be looking
at will be looking at other machines as well in the future. We are
running the sun-release of postgresql 8.1.3 on that T2000 now, but
are looking at compiling the cvs-head version (for its
index-root-cache) somewhere this week.
My guess is there are a few people on this list who are interested
in some dtrace results taken during our benchmarks on that T2000.
Although my knowledge of both Solaris and Dtrace are very limited,
I already took some samples of the system and user calls. I used
Jignesh Shah's scripts for that:
http://blogs.sun.com/roller/page/jkshah?entry=profiling_postgresql_using_dtrace_on
You can find the samples here:
http://achelois.tweakers.net/~acm/pgsql-t2000/syscall.log
http://achelois.tweakers.net/~acm/pgsql-t2000/usrcall.log
And I also did the memcpy-scripts, here:
http://achelois.tweakers.net/~acm/pgsql-t2000/memcpysize.log
http://achelois.tweakers.net/~acm/pgsql-t2000/memcpystack.log
(this last log is 3.5MB)
If anyone is interested in some more dtrace results, let me know
(and tell me what commands to run ;-) ).
Best regards,
Arjen
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