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Message-ID: <536110.72154.qm@web26008.mail.ukl.yahoo.com>
Date: Fri, 4 Mar 2011 17:34:39 +0000 (GMT)
From: Glyn Astill <glynastill@yahoo.co.uk>
Subject: Linux I/O schedulers - CFQ & random seeks
To: pgsql-performance@postgresql.org
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Hi Guys,=0A=0AI'm in the process of setting up some new hardware and am jus=
t doing some basic disk performance testing with bonnie++ to start with.=0A=
=0AI'm seeing a massive difference on the random seeks test, with CFQ not p=
erforming very well as far as I can see.  The thing is I didn't see this so=
rt of massive divide when doing tests with our current hardware.=0A=0ACurre=
nt hardware: 2x4core E5420 @2.5Ghz/ 32GB RAM/ Adaptec 5805Z w' 512Mb/ Raid =
10/ 8 15k 3.5 Disks=0ANew hardware: 4x8core X7550 @2.0Ghz/ 128GB RAM/ H700 =
w' 1GB/ Raid 10/ 12 15.2k 2.5 Disks=0A=0AAdmittedly, my testing on our curr=
ent hardware was on 2.6.26 and on the new hardware it's on 2.6.32 - I think=
 I'm going to have to check the current hardware on the older kernel too.=
=0A=0AI'm wondering (and this may be a can of worms) what peoples opinions =
are on these schedulers?  I'm going to have to do some real world testing m=
yself with postgresql too, but initially was thinking of switching from our=
 current CFQ back to deadline.=0A=0AAny opinions  would be appreciated.=0A=
=0ARegardless, here are some sample results from the new hardware:=0A=0ACFQ=
:=0A=0AVersion  1.96       ------Sequential Output------ --Sequential Input=
- --Random-=0AConcurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- -=
-Block-- --Seeks--=0AMachine        Size K/sec %CP K/sec %CP K/sec %CP K/se=
c %CP K/sec %CP  /sec %CP=0AWay5ax      258376M   666  99 434709  96 225498=
  35  2840  69 952115  76 556.2   3=0ALatency             12344us     619ms=
     522ms     255ms     425ms     529ms=0AVersion  1.96       ------Sequen=
tial Create------ --------Random Create--------=0AWay5ax              -Crea=
te-- --Read--- -Delete-- -Create-- --Read--- -Delete--=0A              file=
s  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP=0A           =
      16 28808  41 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++=0ALate=
ncy              6170us     594us     633us    7619us      20us      36us=
=0A1.96,1.96,Way5ax,1,1299173113,258376M,,666,99,434709,96,225498,35,2840,6=
9,952115,76,556.2,3,16,,,,,28808,41,+++++,+++,+++++,+++,+++++,+++,+++++,+++=
,+++++,+++,12344us,619ms,522ms,255ms,425ms,529ms,6170us,594us,633us,7619us,=
20us,36us=0A=0Adeadline:=0A=0AVersion  1.96       ------Sequential Output--=
---- --Sequential Input- --Random-=0AConcurrency   1     -Per Chr- --Block-=
- -Rewrite- -Per Chr- --Block-- --Seeks--=0AMachine        Size K/sec %CP K=
/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP=0AWay5ax      258376M   69=
6  99 449914  96 287010  47  2952  69 989527  78  2304  19=0ALatency       =
      11939us     856ms     570ms     174ms     228ms   24744us=0AVersion  =
1.96       ------Sequential Create------ --------Random Create--------=0AWa=
y5ax              -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete=
--=0A              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP =
 /sec %CP=0A                 16 31338  45 +++++ +++ +++++ +++ +++++ +++ +++=
++ +++ +++++ +++=0ALatency              5605us     605us     627us    6590u=
s      19us      38us=0A1.96,1.96,Way5ax,1,1299237441,258376M,,696,99,44991=
4,96,287010,47,2952,69,989527,78,2304,19,16,,,,,31338,45,+++++,+++,+++++,++=
+,+++++,+++,+++++,+++,+++++,+++,11939us,856ms,570ms,174ms,228ms,24744us,560=
5us,605us,627us,6590us,19us,38us=0A=0Ano-op:=0A=0AVersion  1.96       -----=
-Sequential Output------ --Sequential Input- --Random-=0AConcurrency   1   =
  -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--=0AMachine    =
    Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP=0AWay5=
ax      258376M   706  99 451578  95 303351  49  4104  96 1003688  78  2294=
  19=0ALatency             11538us     530ms    1460ms   12141us     350ms =
  22969us=0AVersion  1.96       ------Sequential Create------ --------Rando=
m Create--------=0AWay5ax              -Create-- --Read--- -Delete-- -Creat=
e-- --Read--- -Delete--=0A              files  /sec %CP  /sec %CP  /sec %CP=
  /sec %CP  /sec %CP  /sec %CP=0A                 16 31137  44 +++++ +++ ++=
+++ +++ +++++ +++ +++++ +++ +++++ +++=0ALatency              5918us     597=
us     627us    5039us      17us      36us=0A1.96,1.96,Way5ax,1,1299245225,=
258376M,,706,99,451578,95,303351,49,4104,96,1003688,78,2294,19,16,,,,,31137=
,44,+++++,+++,+++++,+++,+++++,+++,+++++,+++,+++++,+++,11538us,530ms,1460ms,=
12141us,350ms,22969us,5918us,597us,627us,5039us,17us,36us=0A=0A--=0AGlyn=0A=
=0A=0A