Linux TPC-C performance aided by kernel features

This past Monday HP released the very first TPC-C benchmark result done using
Linux.  When comparing it to a previous HP result using basically the same
hardware and same database but with Windows 2000, the Linux result is faster
and cheaper.  The benchmark is a proof point that shows Linux can run well in
an enterprise environment.

Of more interest to this mailing list however would be some of the kernel
features that gave us a performance boost.

1. Async IO  - We saw about a 5% increase in performance when using Ben's
asynchronous IO with Oracle.  The peformance gain was because of reduced
overhead on the Oracle and OS process front.  By using async IO we were able
to run with only 2 Oracle dbwriter processes rather than the 15+ we would
have needed without it.  This made the Oracle environment more efficient, and
reduced our context switch overhead on the OS side.

2. Large memory support (16GB) - The Oracle processes used about 14GB of
shared memory which was allocated using shmfs and managed through a mapping
window in the Oracle process space.  Databases always love more memory,
however in an IA-32 architecture the gains definitely diminish once you get
past 4GB because of overhead.  Our gains going from 8GB to 16GB of memory in
the system were in the 10% range.  

3. Raw device access - I don't have a percentage gain for this one since we
have been using this feature since the beginning.  Initial testing last year
showed that raw device access was definitely superior to other methods of
device access.  On a single node, O_DIRECT would be an option now, but for
cluster configurations multinode filesystem access would be needed.  One
limitation we kept running into was the 256 raw device limit imposed by raw
having a single major number.  This issue has been taken care of in 2.5, but
for 2.4 based kernels it is a limitation for larger configurations.

4. 2MB PTE's for Oracle memory - We saw an 8% gain when we switched from
using 4k PTE's to 2MB PTE's for the shared memory Oracle was allocating.
14GB of the 16GB of memory on the system was set aside for this "bigpage"
usage.

Other features such as IO elevator tuning, process priority adjustment, and
TCP tuning were also used.


For those that are interested in more detail about the benchmark
configuration I would refer you to this TPC web page where #7 is the Linux
benchmark and #8 is the Windows one.  You can select the benchmark and pull
up the full disclosure report for more gory detail.

http://www.tpc.org/tpcc/results/tpcc_perf_results.asp?resulttype=cluster

Regards,
Andy

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