[Xapian-discuss] Unexpected slowness

[Arjen van der Meijden]

On 6-2-2007 16:40 Daniel Andersson wrote:
> On 5 Feb 2007, at 20:17, Olly Betts wrote:
> faster as in faster cpu, faster disks and faster memory
> but it only has 1 gb of ram
> it's running on megaraid with scsi-disks. from bonnie++:
> 
> Version  1.03       ------Sequential Output------ --Sequential Input- 
> --Random-
>                     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- 
> --Seeks--
> Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  
> /sec %CP
> septum           2G 14061  54 14601   5  3258   0  5026  16  4289   0 
> 219.7   0
>                     ------Sequential Create------ --------Random 
> Create--------
>                     -Create-- --Read--- -Delete-- -Create-- --Read--- 
> -Delete--
>               files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  
> /sec %CP
>                  16 12837  44 +++++ +++ 14069  57 14783  55 +++++ +++ 
> 12375  59
> septum,2G,14061,54,14601,5,3258,0,5026,16,4289,0,219.7,0,16,12837,44,+++++,+++,14069,57,14783,55,+++++,+++,12375,59 

If I read that correctly, your only reading by about 4-5MB/sec from that 
disk-array? That is not very fast... Last week I did a test (also with 
bonnie++ 1.03) on an array of four 320GB sata disks in raid5 on a LSI 
SATA-8X with 256MB ram (a sata-megaraid controller), which does about 
80MB/sec block reads and something like 40MB/sec for char reads. The 
single 500GB ide-disk that is also in the same box got to 40MB/sec and 
30MB/sec respectively orso.
So my single disk is already 8 times faster in reads and my simple raid 
array 20 times, than your set-up. Writes are also faster on both 
set-ups, but thats a bit skewed since IDE and SATA drives generally lie 
about being finished with their write.

Of course the results of bonnie can vary a bit, depending on concurrent 
work load and the exact set-up, but your set-up doesn't strike me as 
very fast. Perhaps you need to adjust the device's caching strategies, 
but otherwise you may actually be better of with a single modern drive, 
rather than your current array. Of course with a relatively small 
database like your 1.7GB, you can easily add more ram to get the best 
possible performance, since that will always be faster than a fast disk 
set-up, once things are cached.

Best regards,

Arjen