We have severe database performance problems on a K450 with 4 x 160MHz CPUs,
2GB memory and 3 x Model 20 (Nike) disk arrays having 4GB disks. These are
serviced by two FWD busses. No VM activity to speak of.
There are 14 LUNS spread across these arrays, mainly RAID 1. The logical
Sybase devices (raw disk) are arranged over many LUNs to spread the load.
However, two LUNs are taking over 90% of the load! These are in the same
array, but on separate SP controllers. Other disks are barely touched. Read
cache is 50MB per SP and write is 10MB, chosen due to the heavy
read-intensive application (Arbor/BP running on a separate server).
shmmax has been upped from the 10.20 'maximum' of 1GB to 1.74GB - Sybase is
using almost all of this in a couple of big chunks: 1GB & 700MB and a few
smaller ones, according to ipcs -mob.
A simple select count (*) takes forever to return and hits lots of disks
hard, whereas the same query takes 2 minutes on a less powerful K250 with a
dump/loaded copy of the DB.
adb does not run - reason unknown. Simply returns a command prompt.
Now, have we screwed up by setting shmmax too high? If we reset it to 1GB
will Sybase be able to use multiple segments?
Any help gratefully received - thanks in advance.
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