Re: 7.2 or 7.3?

[Florin Andrei]

On Wed, 2002-09-04 at 12:29, Gordon Messmer wrote: 
> 
> I don't know that 7.3 will offer you much, but if you can simulate the
> activity, you might want to try porting to PostgreSQL rather than
> MySQL.  MySQL is reputed to perform very poorly with a large number of
> clients connected, and with a high insert/select ratio, both of which
> describe your installation.  PostgreSQL (might as well run on 7.3, with
> the latest server version) may offer significant performance
> improvements.

That's odd, i'm using it precisely because it has a good INSERT
performance, which corresponds to my tests. 
But indeed, i didn't tested with a large number of connections, so this
might be an avenue... 

> The only thing that I wonder about is that your load is mostly in the
> "system".  You might get better performance by simply adjusting your
> read-ahead and write-cache settings.  Try to figure out how *much* disk
> activity is being generated by the server using "vmstat".

[root@ irq]# vmstat 1
   procs  memoryswap  io
system cpu
 r  b  w   swpd   free   buff  cache  si  sobibo   incs  us 
sy  id
 0  0  0   1152  10916  4 811756   0   0 0 10 2  
4   2   5
 1  0  0   1152  11676  4 811776   0   0 0 0  175  1260   9 
34  57
 0  0  0   1152  10700  4 811796   0   0 0 0  163  1047   6 
32  63
 3  0  0   1152  12484  4 811800   0   0 0 0  141   691   4 
18  78
 0  0  0   1152  10676  4 811812   0   0 0 0  164  1021   9 
21  70
 0  0  0   1152  10684  4 811820   0   0 032  162  1016   5 
25  70
 0  0  0   1152  10672  4 811832   0   0 0 0  162  1038   7 
27  66
 1  0  0   1152  10668  4 811836   0   0 0 0  151   956   6 
24  70
 0  0  0   1152  10664  4 811840   0   0 0 0  137   286  
2   5  93
 0  0  0   1152  10668  4 811852   0   0 0 0  137   542   5 
10  84
 1  0  0   1152  10516  4 811856   0   0 0   156  176   854   7 
17  75
 0  0  0   1152  10640  4 811864   0   0 0 0  158   796   4 
19  77

Seems like there's not much disk IO, but lots of context switches.
Could it be that the system spends too much time just switching between
threads?

-- 
Florin Andrei

"The world is full of bad security systems designed by people
who read 'Applied Cryptography'." - Bruce Schneier



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7.2 or 7.3?

[Florin Andrei]

(i'll describe my situation first, the question is at the end)

I'm running a database server (MySQL) with quite a few connections:

[root@ irq]# ps ax | grep mysqld | wc -l
 67
[root@ irq]#

I suspect the kernel spends a good deal of time in context switches.
There's also some SCSI activity and some network traffic.
The CPU usage is spent mostly in kernel space ("system"); the user space
is tipically not quite so busy.

Basically, the system receives data almost constantly over the network,
via a custom daemon that dispatches it and sends it to MySQL. The
database is doing plain INSERT DELAYED's most of the time (although some
occasional SELECT's are issued from Apache/PHP to spice up things every
now and then).

At this moment, the system runs on Red Hat 7.2 (actually, the SGI patch
with XFS).
My system is a 2xPIII/700, 1 GB RAM, 4x36GB SCSI in a RAID5, Mylex
DAC960.

Are there any serious reasons to upgrade to 7.3?
Does the kernel in 7.3 has some clear improvements over the 7.2 that
make a difference in my situation? If that's true, what are those
improvements?

-- 
Florin Andrei

"The world is full of bad security systems designed by people
who read 'Applied Cryptography'." - Bruce Schneier



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