On Thu, Aug 17, 2006 at 10:57:46AM -0400, David Boyes wrote:
> The way QDIO device handling works, the size of the transfer buffers
> affect the amount of information that can be moved with a single
> operation, which sets a maximum limit on the transfer rate for a fixed
> processor speed.
>
> Analagous to DMA buffer size; not main storage allocation, but managing
> link congestion by controlling transmit/receive buffers and window size.
Well, yes, but my point is that (especially for database aplications) often
the problem with I/O wait times is related to engine tuning rather than I/O
channel speed. Essentially, if the database is optimally tuned and has a
working set that can fit in core memory, the I/O channel speed becomes less
of an issue because less real I/O will be needed once a stable state has
been reached. It's one of the oldest (and most influencial) performance
tuning tricks in the database world ;)
Most databases that are dependent on I/O speed are bound to perform slowly
because I/O is, well, slow :)
Kris
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