Hmmm... So are you saying that "GROUP BY" operations use the CPU cache to a larger
extent than other operations? (Is this documented somewhere?)
Don't forget that the other 80-odd operations listed in the benchmark are actually
faster on the new machine. It's odd that only these "GROUP BY" type operations are
slower on the new box! They must use the hardware in a different way?
Here is a summary of what I see regarding the CPU cache (from dmesg). Do you think
these figures support your theory? (I'm not sure how Athlons compare to Xeons?) Note
that the new CPU's have twice the amount of level 2 cache.
The old box (2 CPU's):
CPU: L1 I Cache: 64K (64 bytes/line), D cache 64K (64 bytes/line)
CPU: L2 Cache: 256K (64 bytes/line)
CPU0: AMD Athlon(tm) MP 2000+ stepping 02
per-CPU timeslice cutoff: 731.44 usecs.
CPU1: AMD Athlon(tm) MP stepping 02
..... CPU clock speed is 1666.7119 MHz.
And the new box (4 CPU's):
CPU: L1 I cache: 12K, L1 D cache: 8K
CPU: L2 cache: 512K
CPU0: Intel(R) Xeon(TM) CPU 2.80GHz stepping 09
per-CPU timeslice cutoff: 1463.10 usecs.
CPU3: Intel(R) Xeon(TM) CPU 2.80GHz stepping 09
..... CPU clock speed is 2793.7204 MHz.
Thanks for your advice everyone!
Tony
Ps. Good suggestion Donny, but both /tmp's are ext3. (And the new /tmp is faster,
based on this little test: rm -f ttt; sync; sync; time dd if=/dev/zero of=./ttt bs=16M
count=32)
Kevin Cowley wrote:
> Don't tell me - you upgraded a PIII server to a PIV server?
> The cache on the PIV is les than half the size of a PIII.
>
> We've hit this problem with our own apps that by the way they operate cache
> a lot of data. A PIII 1.4GHz will match a 2.4 GHz PIV.
Yes, MySQL code is written with a lot of care to use the CPU cache efficiently.
Having a larger cache will compensate for the lack of CPU speed to a great
extent. So the results do look about right.
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