2011/9/14 Michał Piotrowski <mkkp4x4@xxxxxxxxx>
Okay... brace yourself.
I just ran this test on my non-SSD ext4 based F15 system and I get the opposite result on start...repeatably. On my system the systemd based start up in the admittedly simple service postgresql start testing is consistently faster by about a second. And just as interesting... my sysinit times are slower than yours, that's a real head scratcher for me. If my db test was less overall work to init for some reason I'd expect my numbers to be faster than yourse in both cases. I have no off the top of my head theory that could explain that except that your low level disk i/o is significantly different than mine.
Both variants of "service postgresql stop" is within a 1/10 of a second in my testing
I can give you the screen log captures for my tests if you desire to review my actions but here here is the summary for my simple timing test: And admittedly I'm using a simply initiated postgres db. It could be that your real world database initialization workload is more intensive than my test and the disk i/o is now a limiting factor in a different way.
And of course my numbers do not discount what your seeing as my test is as anecdotal as your is. Your numbers may still be indicative of a more nuanced problem that can be resolved and its good to have your numbers as a starting point for a discussion around understanding optimization issues (like disk i/o). We just can't jump to conclusions about why you are seeing what your are seeing. I hope my numbers serve as a cautionary reminder to those others on this list that benchmarking disk io intensive tasks can be very complex and very system dependent. Certain other people in this discussion are being overly bombastic and seem to have forgotten this fact. I hope for all our sakes they can find a way to ratchet down the hyperbole and look at these sort of issues with a more clinical approach.
Okay so here's my summary of the quick tests. Please if you have an updated methodology for me to test, let me know. I'm willing to reuse a specially crafted pgsql database if you feel that will help you. Though I'd think we wan't to do that sort of deep dive comparison off list until we are ready to publish some summaries after we both feel comfortable with the test runs.
-jef
==========================================
SysVinit:
service postgresql status
postgresql.service - LSB: start and stop PostgreSQL server
Loaded: loaded (/etc/rc.d/init.d/postgresql)
Active: inactive (dead)
CGroup: name=systemd:/system/postgresql.service
time service postgresql start
real 0m2.329s
user 0m0.028s
sys 0m0.046s
time service postgresql stop
real 0m1.281s
user 0m0.035s
sys 0m0.096s
time service postgresql start
real 0m2.242s
user 0m0.031s
sys 0m0.038s
time service postgresql stop
real 0m1.235s
user 0m0.031s
sys 0m0.036s
=========================================
Systemd based:
status postgresql.service
postgresql.service - PostgreSQL database server
Loaded: loaded (/lib/systemd/system/postgresql.service)
Active: inactive (dead)
CGroup: name=systemd:/system/postgresql.service
time service postgresql start
real 0m1.141s
user 0m0.019s
sys 0m0.019s
time service postgresql stop
real 0m1.146s
user 0m0.017s
sys 0m0.017s
time service postgresql start
real 0m1.153s
user 0m0.016s
sys 0m0.019s
time service postgresql stop
real 0m1.144s
user 0m0.026s
sys 0m0.014s
Exactly. F15, PostgreSQL 9.0 and just service file from PostgreSQL
9.1. Root filesystem and database are on SSD and Ext4.
Okay... brace yourself.
I just ran this test on my non-SSD ext4 based F15 system and I get the opposite result on start...repeatably. On my system the systemd based start up in the admittedly simple service postgresql start testing is consistently faster by about a second. And just as interesting... my sysinit times are slower than yours, that's a real head scratcher for me. If my db test was less overall work to init for some reason I'd expect my numbers to be faster than yourse in both cases. I have no off the top of my head theory that could explain that except that your low level disk i/o is significantly different than mine.
Both variants of "service postgresql stop" is within a 1/10 of a second in my testing
I can give you the screen log captures for my tests if you desire to review my actions but here here is the summary for my simple timing test: And admittedly I'm using a simply initiated postgres db. It could be that your real world database initialization workload is more intensive than my test and the disk i/o is now a limiting factor in a different way.
And of course my numbers do not discount what your seeing as my test is as anecdotal as your is. Your numbers may still be indicative of a more nuanced problem that can be resolved and its good to have your numbers as a starting point for a discussion around understanding optimization issues (like disk i/o). We just can't jump to conclusions about why you are seeing what your are seeing. I hope my numbers serve as a cautionary reminder to those others on this list that benchmarking disk io intensive tasks can be very complex and very system dependent. Certain other people in this discussion are being overly bombastic and seem to have forgotten this fact. I hope for all our sakes they can find a way to ratchet down the hyperbole and look at these sort of issues with a more clinical approach.
Okay so here's my summary of the quick tests. Please if you have an updated methodology for me to test, let me know. I'm willing to reuse a specially crafted pgsql database if you feel that will help you. Though I'd think we wan't to do that sort of deep dive comparison off list until we are ready to publish some summaries after we both feel comfortable with the test runs.
-jef
==========================================
SysVinit:
service postgresql status
postgresql.service - LSB: start and stop PostgreSQL server
Loaded: loaded (/etc/rc.d/init.d/postgresql)
Active: inactive (dead)
CGroup: name=systemd:/system/postgresql.service
time service postgresql start
real 0m2.329s
user 0m0.028s
sys 0m0.046s
time service postgresql stop
real 0m1.281s
user 0m0.035s
sys 0m0.096s
time service postgresql start
real 0m2.242s
user 0m0.031s
sys 0m0.038s
time service postgresql stop
real 0m1.235s
user 0m0.031s
sys 0m0.036s
=========================================
Systemd based:
status postgresql.service
postgresql.service - PostgreSQL database server
Loaded: loaded (/lib/systemd/system/postgresql.service)
Active: inactive (dead)
CGroup: name=systemd:/system/postgresql.service
time service postgresql start
real 0m1.141s
user 0m0.019s
sys 0m0.019s
time service postgresql stop
real 0m1.146s
user 0m0.017s
sys 0m0.017s
time service postgresql start
real 0m1.153s
user 0m0.016s
sys 0m0.019s
time service postgresql stop
real 0m1.144s
user 0m0.026s
sys 0m0.014s
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