Re: 2x Oracle slowdown from 2.2.16 to 2.4.4

[Lance Larsh <Lance.Larsh@oracle.com>]

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Andi Kleen wrote:

> My understanding is that this is normally true for Oracle, but probably
> not for iozone so it would be better if you benchmarked random writes
> to an already allocated file.

You are correct that this is true for Oracle:  we preallocate the file at db create
time, and we use O_DSYNC to avoid atime updates.  The same is true for iozone:  it
performs writes to all the blocks (creating the file and allocating blocks), then
rewrites all of the blocks.  The write and rewrite times are measured and reported
in separate.  Naturally, we only care about the rewrite times, and those are the
results I'm quoting when I casually use the term "writes".  Also, we pass the "-o"
option to iozone, which causes it to open the file with O_SYNC (which on Linux is
really O_DSYNC), just like Oracle does.  So, the mode I'm running iozone in really
does model Oracle i/o.  Sorry if that wasn't clear.

Thanks,
Lance



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