Re: Commit slower on faster PC

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 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)
>
> 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 on 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 following log 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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