Thread: Commit slower on faster PC

Commit slower on faster PC

From
"Koth, Christian (DWBI)"
Date:
Hi,

please help me with the following problem:

I have noticed a strange performance behaviour using a commit statement on two different machines. On one of the
machinesthe commit is many times faster than on the other machine which has faster hardware. Server and client are
runningalways on the same machine. 

Server version (same on both machines): PostgreSQL 8.1.3. (same binaries as well)

PC1:
----
Pentium 4 (2.8 GHz)
1GB RAM
IDE-HDD (approx. 50 MB/s rw), fs: ext3
Mandrake Linux: Kernel 2.4.22


PC2:
----
Pentium 4 (3.0 GHz)
2GB RAM
SCSI-HDD (approx. 65 MB/s rw), fs: ext3
Mandrake Linux: Kernel 2.4.32


Both installations of the database have the same configuration, different from default are only the following settings
onboth machines: 

shared_buffers = 20000
listen_addresses = '*'
max_stack_depth = 4096


pgbench gives me the following results:
PC1:
----
transaction type: TPC-B (sort of)
scaling factor: 1
number of clients: 1
number of transactions per client: 10
number of transactions actually processed: 10/10
tps = 269.905533 (including connections establishing)
tps = 293.625393 (excluding connections establishing)

PC2:
----
transaction type: TPC-B (sort of)
scaling factor: 1
number of clients: 1
number of transactions per client: 10
number of transactions actually processed: 10/10
tps = 46.061935 (including connections establishing)
tps = 46.519634 (excluding connections establishing)


My own performance test sql script which inserts and (auto)commits some data into a simple table produces the following
logoutput in the server log: 

PC1:
----
LOG:  duration: 1.441 ms  statement: INSERT INTO performance_test VALUES (500938362, 'Xawhefjmd');
STATEMENT:  INSERT INTO performance_test VALUES (500938362, 'Xawhefjmd');

PC2:
----
LOG:  duration: 29.979 ms  statement: INSERT INTO performance_test VALUES (500938362, 'Xawhefjmd');
STATEMENT:  INSERT INTO performance_test VALUES (500938362, 'Xawhefjmd');


I created a 'strace' one both machines which is interesting:

Opening the socket:
-------------------
PC1: socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 10 <0.000021>
PC2: socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 8 <0.000015>

PC1: bind(10, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("0.0.0.0")}, 16) = 0 <0.000007>
PC2: bind (8, {sin_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("0.0.0.0")}}, 16) = 0 <0.000007>

PC1: getsockname(10, {sa_family=AF_INET, sin_port=htons(32820), sin_addr=inet_addr("0.0.0.0")}, [16]) = 0 <0.000005>
PC2: getsockname( 8, {sin_family=AF_INET, sin_port=htons(36219), sin_addr=inet_addr("0.0.0.0")}}, [16]) = 0 <0.000005>

PC1: connect(10, {sa_family=AF_INET, sin_port=htons(5432), sin_addr=inet_addr("127.0.0.1")}, 16) = 0 <0.000440>
PC2: connect( 8, {sin_family=AF_INET, sin_port=htons(5432), sin_addr=inet_addr("127.0.0.1")}}, 16) = 0 <0.000394>

PC1: setsockopt(10, SOL_TCP, TCP_NODELAY, [1], 4) = 0 <0.000006>
PC2: setsockopt (8, SOL_TCP, TCP_NODELAY, [1], 4) = 0 <0.000004>


Inserting and commiting the data: <exec. time>
---------------------------------
PC1:
----
send(10, "B\....\0<\0INSERT INTO performance_test VAL"..., 175, 0) = 175 <0.000015>
recv(10, "2\....0\17INSERT 0 1\0Z\0\0\0\5T", 8192, 0) = 53 <0.000007>
send(10, "B\0\0\0\17\0S_2\0\0\0\0\0\0\0E\0\0\0\t\0\0\0\0\1S\0\0\0\4", 31, 0) = 31 <0.000011>
recv(10, "2\0\0\0\4C\0\0\0\vCOMMIT\0Z\0\0\0\5I", 8192, 0) = 23 <0.000211>

PC2:
----
send(8, "B\....\0<\0INSERT INTO performance_test VAL"..., 175, 0) = 175 <0.000014>
recv(8, "2\....0\17INSERT 0 1\0Z\0\0\0\5T", 8192, 0) = 53 <0.000005>
send(8, "B\0\0\0\17\0S_2\0\0\0\0\0\0\0E\0\0\0\t\0\0\0\0\1S\0\0\0\4", 31, 0) = 31 <0.000009>
recv(8, "2\0\0\0\4C\0\0\0\vCOMMIT\0Z\0\0\0\5I", 8192, 0) = 23 <0.0253>

Every command is a bit faster on PC2 except the last one which is many times slower.
Any help or hint where to look at would be highly appreciated because I'm running out of ideas ;-).


regards,
Christian


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Re: Commit slower on faster PC

From
Mark Lewis
Date:
The IDE drive is almost certainly lying about flushing data to the disk.
Lower-end consumer drives often do.

What this means is that commits will be a whole lot faster, but the
database loses its ACID guarantees, because a power failure at the wrong
moment could corrupt the whole database.

If you don't care about your data and want the SCSI drive to perform
fast just like the IDE drive, you can set fsync = off in your
configuration file.

-- Mark

On Wed, 2006-07-12 at 10:16 -0600, Koth, Christian (DWBI) wrote:
> Hi,
>
> please help me with the following problem:
>
> I have noticed a strange performance behaviour using a commit statement on two different machines. On one of the
machinesthe commit is many times faster than on the other machine which has faster hardware. Server and client are
runningalways on the same machine. 
>
> Server version (same on both machines): PostgreSQL 8.1.3. (same binaries as well)
>
> PC1:
> ----
> Pentium 4 (2.8 GHz)
> 1GB RAM
> IDE-HDD (approx. 50 MB/s rw), fs: ext3
> Mandrake Linux: Kernel 2.4.22
>
>
> PC2:
> ----
> Pentium 4 (3.0 GHz)
> 2GB RAM
> SCSI-HDD (approx. 65 MB/s rw), fs: ext3
> Mandrake Linux: Kernel 2.4.32
>
>
> Both installations of the database have the same configuration, different from default are only the following
settingson both machines: 
>
> shared_buffers = 20000
> listen_addresses = '*'
> max_stack_depth = 4096
>
>
> pgbench gives me the following results:
> PC1:
> ----
> transaction type: TPC-B (sort of)
> scaling factor: 1
> number of clients: 1
> number of transactions per client: 10
> number of transactions actually processed: 10/10
> tps = 269.905533 (including connections establishing)
> tps = 293.625393 (excluding connections establishing)
>
> PC2:
> ----
> transaction type: TPC-B (sort of)
> scaling factor: 1
> number of clients: 1
> number of transactions per client: 10
> number of transactions actually processed: 10/10
> tps = 46.061935 (including connections establishing)
> tps = 46.519634 (excluding connections establishing)
>
>
> My own performance test sql script which inserts and (auto)commits some data into a simple table produces the
followinglog output in the server log: 
>
> PC1:
> ----
> LOG:  duration: 1.441 ms  statement: INSERT INTO performance_test VALUES (500938362, 'Xawhefjmd');
> STATEMENT:  INSERT INTO performance_test VALUES (500938362, 'Xawhefjmd');
>
> PC2:
> ----
> LOG:  duration: 29.979 ms  statement: INSERT INTO performance_test VALUES (500938362, 'Xawhefjmd');
> STATEMENT:  INSERT INTO performance_test VALUES (500938362, 'Xawhefjmd');
>
>
> I created a 'strace' one both machines which is interesting:
>
> Opening the socket:
> -------------------
> PC1: socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 10 <0.000021>
> PC2: socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 8 <0.000015>
>
> PC1: bind(10, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("0.0.0.0")}, 16) = 0 <0.000007>
> PC2: bind (8, {sin_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("0.0.0.0")}}, 16) = 0 <0.000007>
>
> PC1: getsockname(10, {sa_family=AF_INET, sin_port=htons(32820), sin_addr=inet_addr("0.0.0.0")}, [16]) = 0 <0.000005>
> PC2: getsockname( 8, {sin_family=AF_INET, sin_port=htons(36219), sin_addr=inet_addr("0.0.0.0")}}, [16]) = 0
<0.000005>
>
> PC1: connect(10, {sa_family=AF_INET, sin_port=htons(5432), sin_addr=inet_addr("127.0.0.1")}, 16) = 0 <0.000440>
> PC2: connect( 8, {sin_family=AF_INET, sin_port=htons(5432), sin_addr=inet_addr("127.0.0.1")}}, 16) = 0 <0.000394>
>
> PC1: setsockopt(10, SOL_TCP, TCP_NODELAY, [1], 4) = 0 <0.000006>
> PC2: setsockopt (8, SOL_TCP, TCP_NODELAY, [1], 4) = 0 <0.000004>
>
>
> Inserting and commiting the data: <exec. time>
> ---------------------------------
> PC1:
> ----
> send(10, "B\....\0<\0INSERT INTO performance_test VAL"..., 175, 0) = 175 <0.000015>
> recv(10, "2\....0\17INSERT 0 1\0Z\0\0\0\5T", 8192, 0) = 53 <0.000007>
> send(10, "B\0\0\0\17\0S_2\0\0\0\0\0\0\0E\0\0\0\t\0\0\0\0\1S\0\0\0\4", 31, 0) = 31 <0.000011>
> recv(10, "2\0\0\0\4C\0\0\0\vCOMMIT\0Z\0\0\0\5I", 8192, 0) = 23 <0.000211>
>
> PC2:
> ----
> send(8, "B\....\0<\0INSERT INTO performance_test VAL"..., 175, 0) = 175 <0.000014>
> recv(8, "2\....0\17INSERT 0 1\0Z\0\0\0\5T", 8192, 0) = 53 <0.000005>
> send(8, "B\0\0\0\17\0S_2\0\0\0\0\0\0\0E\0\0\0\t\0\0\0\0\1S\0\0\0\4", 31, 0) = 31 <0.000009>
> recv(8, "2\0\0\0\4C\0\0\0\vCOMMIT\0Z\0\0\0\5I", 8192, 0) = 23 <0.0253>
>
> Every command is a bit faster on PC2 except the last one which is many times slower.
> Any help or hint where to look at would be highly appreciated because I'm running out of ideas ;-).
>
>
> regards,
> Christian
>
>
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Re: Commit slower on faster PC

From
"D'Arcy J.M. Cain"
Date:
On Wed, 12 Jul 2006 10:16:40 -0600
"Koth, Christian (DWBI)" <Christian.Koth@smiths-heimann.com> wrote:
> I have noticed a strange performance behaviour using a commit statement on two different machines. On one of the
machinesthe commit is many times faster than on the other machine which has faster hardware. Server and client are
runningalways on the same machine. 
>
> Server version (same on both machines): PostgreSQL 8.1.3. (same binaries as well)
>
> PC1:
> ----
> Pentium 4 (2.8 GHz)
> 1GB RAM
> IDE-HDD (approx. 50 MB/s rw), fs: ext3
> Mandrake Linux: Kernel 2.4.22
>
>
> PC2:
> ----
> Pentium 4 (3.0 GHz)
> 2GB RAM
> SCSI-HDD (approx. 65 MB/s rw), fs: ext3
> Mandrake Linux: Kernel 2.4.32
>
>
> Both installations of the database have the same configuration, different from default are only the following
settingson both machines: 
>
> shared_buffers = 20000
> listen_addresses = '*'
> max_stack_depth = 4096
>
>
> pgbench gives me the following results:
> PC1:
> ----
> transaction type: TPC-B (sort of)
> scaling factor: 1
> number of clients: 1
> number of transactions per client: 10
> number of transactions actually processed: 10/10
> tps = 269.905533 (including connections establishing)
> tps = 293.625393 (excluding connections establishing)
>
> PC2:
> ----
> transaction type: TPC-B (sort of)
> scaling factor: 1
> number of clients: 1
> number of transactions per client: 10
> number of transactions actually processed: 10/10
> tps = 46.061935 (including connections establishing)
> tps = 46.519634 (excluding connections establishing)

I'm not sure 10 transactions is enough of a test.  You could just be
seeing the result of your IDE drive lying to you about actually writing
your data.  There may be other considerations but I would start with
checking with 10,000 or 100,000 transactions to overcome the driver
buffering.

--
D'Arcy J.M. Cain <darcy@druid.net>         |  Democracy is three wolves
http://www.druid.net/darcy/                |  and a sheep voting on
+1 416 425 1212     (DoD#0082)    (eNTP)   |  what's for dinner.

Re: Commit slower on faster PC

From
"Joshua D. Drake"
Date:
On Wednesday 12 July 2006 09:16, Koth, Christian (DWBI) wrote:
> Hi,
>
> please help me with the following problem:
>
> I have noticed a strange performance behaviour using a commit statement on
> two different machines. On one of the machines the commit is many times
> faster than on the other machine which has faster hardware. Server and
> client are running always on the same machine.
>
> Server version (same on both machines): PostgreSQL 8.1.3. (same binaries as
> well)

Heh, I bet you are being bit by the cache on the IDE drive. What happens if
you turn fsync off?

Sincerely,

Joshua D. Drake
--
   === The PostgreSQL Company: Command Prompt, Inc. ===
Sales/Support: +1.503.667.4564 || 24x7/Emergency: +1.800.492.2240
   Providing the most comprehensive  PostgreSQL solutions since 1997
             http://www.commandprompt.com/



Re: Commit slower on faster PC

From
Bruno Wolff III
Date:
On Wed, Jul 12, 2006 at 10:16:40 -0600,
  "Koth, Christian (DWBI)" <Christian.Koth@smiths-heimann.com> wrote:
>
> I have noticed a strange performance behaviour using a commit statement on two different machines. On one of the
machinesthe commit is many times faster than on the other machine which has faster hardware. Server and client are
runningalways on the same machine. 
>
> Server version (same on both machines): PostgreSQL 8.1.3. (same binaries as well)
>
> PC1:
> ----
> IDE-HDD (approx. 50 MB/s rw), fs: ext3
>
> PC2:
> ----
> SCSI-HDD (approx. 65 MB/s rw), fs: ext3
>
> Both installations of the database have the same configuration, different from default are only the following
settingson both machines: 
>
> pgbench gives me the following results:
> PC1:
> ----
> tps = 293.625393 (excluding connections establishing)
>
> PC2:
> ----
> tps = 46.519634 (excluding connections establishing)

Have you checked to see if the ide drive is lying about having written the
data to the platters?

Re: Commit slower on faster PC

From
"Koth, Christian (DWBI)"
Date:
Hello all,
thanks a lot for your help so far. You all where right about the IDE drive is
somehow caching the data. See the test results below. I also get different 
tps values every time I run pgbench on PC1 (between 300 and 80 tps for 100 transactions).

I don't think it's a good idea to disable fsync even if ext3 (doing a sync also
every x second or so) and a UPS is used.

Christian



PC1 (IDE):
----------

fsynch on:
----------
number of transactions per client: 100
number of transactions actually processed: 100/100
tps = 213.115558 (including connections establishing)
tps = 214.710227 (excluding connections establishing)

number of transactions per client: 10000
number of transactions actually processed: 10000/10000
tps = 126.159130 (including connections establishing)
tps = 126.163172 (excluding connections establishing)


fsynch off:
-----------
number of transactions per client: 100
number of transactions actually processed: 100/100
tps = 413.849044 (including connections establishing)
tps = 419.028942 (excluding connections establishing)

number of transactions per client: 10000
number of transactions actually processed: 10000/10000
tps = 166.057838 (including connections establishing)
tps = 166.064227 (excluding connections establishing)



PC2 (SCSI):
-----------

fsynch on:
----------
number of transactions per client: 100
number of transactions actually processed: 100/100
tps = 44.640785 (including connections establishing)
tps = 44.684649 (excluding connections establishing)

number of transactions per client: 10000
number of transactions actually processed: 10000/10000
tps = 42.322486 (including connections establishing)
tps = 42.324096 (excluding connections establishing)


fsynch off:
-----------
number of transactions per client: 100
number of transactions actually processed: 100/100
tps = 910.406861 (including connections establishing)
tps = 925.428936 (excluding connections establishing)

number of transactions per client: 10000
number of transactions actually processed: 10000/10000
tps = 957.376543 (including connections establishing)
tps = 957.603815 (excluding connections establishing)

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systemand notify your system manager.  Please do not copy it for any purpose, or disclose its contents to any other
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companyaccepts no liability for any damage caused, directly or indirectly, by any virus transmitted in this email. 
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